Substrate Specificity of Rabbit Aldehyde Oxidase for Nitroguanidine and Nitromethylene Neonicotinoid Insecticides

The nitroguanidine or nitromethylene moiety of the newest major class of insecticides, the neonicotinoids, is important for potency at insect nicotinic receptors and selectivity relative to mammalian receptors. Aldehyde oxidase (AOX) was recently identified as the imidacloprid nitroreductase of mammalian liver, producing both nitrosoguanidine and aminoguanidine metabolites. The present study considers the ability of AOX, partially purified from rabbit liver, to reduce five commercial nitroguanidine (i.e., imidacloprid, thiamethoxam, clothianidin, and dinotefuran) and nitromethylene (i.e., nitenpyram) neonicotinoid insecticides and three derivatives thereof (i.e., the N-methyl and nitromethylene analogues of imidacloprid and desmethylthiamethoxam). LC/MS/MS was used to demonstrate that AOX reduces nitroguanidines to both nitroso- and aminoguanidines, while nitromethylenes are reduced only to the corresponding nitroso metabolites. Additionally, nitrosonitenpyram was found to spontaneously dehydrate to form a 2-cyanoamidine metabolite, mimicking a predominant photoreaction. The substrate specificity of AOX was characterized as follows: Neonicotinoids with a tertiary nitrogen (N-methylimidacloprid and thiamethoxam) are poor substrates; nitroguanidines are metabolized faster than nitromethylenes; and clothianidin is the most rapidly reduced. Kinetic constants were measured for reduction of three nitroguanidines at two concentrations of AOX. At 2 mg protein/mL, only nitroso metabolites were detected, with Km values of 1.03, 2.99, and 2.41 mM and Vmax values of 5.13, 2.54, and 0.98 nmol/min/mg protein measured for clothianidin, imidacloprid, and dinotefuran, respectively. At 5 mg protein/mL, both amino and nitroso metabolites were detected. However, with each nitroguanidine, the formation of nitroso metabolites did not saturate at substrate levels up to 4 mM, whereas amino metabolite formation exhibited Km values of 0.052, 0.16, and 0.084 mM with corresponding Vmax values of 0.80, 1.24, and 0.79 nmol/min/mg protein for clothianidin, imidacloprid, and dinotefuran, respectively. These in vitro observations show large structural differences in the rates of AOX-catalyzed reduction and help to interpret the extensive studies on in vivo metabolism of neonicotinoid insecticides.

Detection of N-nitrosomelatonin and other N-nitrosotryptophan derivatives by transnitrosation of APF and DAF-2

S-nitrosothiols can be analyzed with some simple detection procedures and this fact strongly accelerated the understanding of the biological impact of S-nitrosothiols. Unfortunately, such simple analytic methods are presently missing for low molecular weight N-nitrosotryptophan derivatives like N-nitrosomelatonin (NOMela). Here we demonstrate that commercially available primary aromatic amines, i.e. aminophenylfluorescein (APF) and 4,5-diaminofluorescin (DAF-2), can be used for a quantitative determination of NOMela. Under optimized conditions (e.g. pH 11) of the assays, the lifetime of N-nitrosotryptophan derivatives is largely prolonged and the reactivity of S-nitrosothiols with aromatic amines can be safely ignored. The influence of reactive nitrogen oxide species like N2O3 is additionally limited at the alkaline pH and may be further decreased by working under hypoxic conditions. As a result of these optimal conditions, the APF assay has a detection limit for NOMela of about 25 nm but this assay fails to detect protein-bound N-nitrosotryptophan residues. The DAF-2 assay, however, might be used for a qualitative analysis of such residues. Due to the high efficacy of the APF assay it is safely demonstrated that in regard to peroxynitrite, N2O3 is about 50-fold more effective in nitrosating melatonin at physiological pH.

Comparative analysis of tobacco-specific nitrosamines and total N-nitroso compounds in moldovan cigarette tobacco

While previous studies have evaluated levels of tobacco-specific nitrosamines (TSNA) and total N-nitroso compounds (NOC) in tobacco, there are no reports in the literature on TSNA and total NOC in the same tobacco products. We compared levels of TSNA, total NOC, and NOC precursors (NOCP) in tobacco of cigarettes purchased in Moldova and in some tobacco types commonly used for the manufacturing of Moldovan cigarettes. Cigarette tobaccos included those from non-Moldovan, traditional Moldovan, and blended Moldovan cigarettes. The results demonstrate that tobacco of non-Moldovan cigarettes contains higher TSNA and NOC levels (mean, 16 and 63 nmol/g tobacco, n = 6) than that of Moldovan cigarettes (mean, 5 and 23 nmol/g tobacco, n = 25). TSNA and NOC levels were also generally higher in tobacco of blended than in traditional Moldovan cigarettes. NOCP levels in Moldovan and non-Moldovan cigarette tobacco were similar as follows: 29000 +/- 30000 and 33000 +/- 28000 nmol/g tobacco (mean +/- SD). Total NOC were strongly correlated with total TSNA levels (r = 0.66; P < 0.0001). These findings demonstrate that current technologies involved in the manufacture of some blended cigarettes create conditions that favor N-nitrosation of alkaloids and other tobacco constituents.

Development of a food frequency questionnaire module and databases for compounds in cooked and processed meats

There is ample evidence from basic research and animal carcinogenicity studies that heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are mutagens and carcinogens. However, there was a paucity of human data due to a lack of appropriate investigative tools. We developed the first validated cooked meat module within a food frequency questionnaire (FFQ) in the United States of America and created databases to be used in conjunction with this FFQ to estimate intake of HCAs and benzo[a]pyrene, a marker of PAHs. It became clear that other aspects of meat may also contribute to carcinogenesis; in particular, we are pursuing two additional areas: processed meat and iron exposure in relation to cancer risk. To investigate these hypotheses, we have expanded the cooked meat module to include detailed information on processed meats and fish. In addition, we are developing two databases, one for total iron and heme iron in cooked meat and the other for nitrite, nitrate, and N-nitroso compounds in processed meats. In this report, we will outline the methods used to develop the meat questionnaires, the databases, a software package for generating the intake values, and the methods used to generate nutritional data from nationally representative samples.

Determination of total N-nitroso compounds by chemical denitrosation using CuCl

A method for the determination of total N-nitroso compounds (NOC) by chemical denitrosation and subsequent chemiluminescence detection of evolved NO is described. Denitrosation was accomplished with CuCl in HCl at 70 degrees C. The detection limit for N-nitrosoproline (NPRO) was 1 pmol. NO formation from NPRO was linear (R(2) = 0.999) from 4 pmol to 2 nmol. Among the possible interfering compounds tested, only S-nitroso compounds contribute any significant interference. This method had several advantages over other similar methods: (1) A commercially available one-piece reaction vessel and a NO analyzer with software were used. (2) NO release occurred rapidly and was easily measured and quantified. (3) Compared to HBr or HI, CuCl was more convenient to work with and safe. (4) CuCl was suitable for samples in aqueous and most organic solvents. The application of this method to food, personal care products, and human body fluids demonstrates its utility.

Influence of the order of reagent addition on NDMA formation during chloramination

The formation of the potent carcinogen, N-nitrosodimethylamine (NDMA), during chlorine disinfection has caused significant concern among drinking water and wastewater recycling utilities practicing intentional or unintentional chloramination. Previous research modeled NDMA formation as arising from a reaction between monochloramine and organic nitrogen precursors, such as dimethylamine, via an unsymmetrical dimethylhydrazine (UDMH) intermediate. Contrary to the importance of monochloramine indicated by previous studies, hypochlorite formed an order of magnitude more NDMA than monochloramine when applied to a secondary municipal wastewater effluent containing excess ammonia. Experiments involving variation of the order that each reagent (i.e., hypochlorite, ammonium chloride, and dimethylamine) was added to solution suggest two factors that may be more important for NDMA formation than the presence of monochloramine: (i) the chlorination state of organic nitrogen precursors and (ii) the partial formation of dichloramine. Although dichloramine formation was most influenced by the pH conditions under which inorganic chloramine formation was performed, mixing effects related to the order of reagent addition may be important at full-scale plants. Chloramination strategies are suggested that may reduce NDMA formation by nearly an order of magnitude.

[Study on N-nitroso compound in food and its relevant risk factors for esophageal cancer]

OBJECTIVE

To study multiple risk factors of N-nitroso compounds (NOC) in high- and low-risk areas for esophageal cancer in southern China.

METHOD

The samples of 24-hr diets and 12-hr overnight urine were collected from 120 male healthy subjects (35-64 years old) selected by a 3-stage random cluster sample procedure in each of the high-risk area (Nanao County) and low-risk area (Lufeng County) for esophageal cancer. The urinary samples were respectively collected from undosed subjects, subjects ingested 500 mg L-proline (together with 200 mg ascorbic acid ) and subjects ingested 500 mg proline. The levels of total NOC (TNOC), N-nitrosamino acids (NAAs), volatile N-nitroso compounds and reductive ascorbic acid (VC) in the samples were measured. By unconditional logistic stepwise regression model, we analyzed the association between the multiple factors of NOC and esophageal cancer mortality. The factors included the intake and excretion levels of various kinds of NOC, the ability of NAAs endogenous formation and its inhibition by VC, and nutrition status of VC in the body.

RESULTS

The results of unconditional logistic stepwise regression showed that risk factors entered the model were diet TNOC content (OR 9.613, 95% CI 1.921-48.115) and urinary NAAs level after ingested VC (OR 1.137, 95 % CI 1.001-1.298).

CONCLUSION

The higher level of diet TNOC and the lower inhibition ability of NOC endogenous formation by VC were important risk factors on NOC etiology of esophageal cancer in southern China.

N-nitrosylation potential of mono-N-desethylamiodarone at physiological pH

Amiodarone (AMI) is frequently used for the treatment of supraventricular arrhythmias. The parent drug is rapidly dealkylated to mono-N-desethylamiodarone (MDEA) and the plasma concentrations of AMI and MDEA are comparable. MDEA is a secondary amine and may thus undergo formation to the corresponding N-nitrosamine in combination with coadministered nitrovasodilators. Previous studies have shown that nitrovasodilators release the vasoactive NO? which may nitrosylate thiol or secondary amine groups in aqueous solutions. Therefore, the nitrosylation potential of MDEA at physiological pH was investigated. N-Nitroso-monodesethylamiodarone (NO-MDEA) was synthesized, characterized and used as a reference product for the detection of the corresponding N-nitrosamine. HPLC and NMR results have shown that the NO-MDEA product is an equilibrium of two configurational isomers (syn and anti). NO-release was generated by sodium nitroprusside (SNP) which was exposed to light. The formation to NO-MDEA was assayed by HPLC-UV. It has been found that MDEA is nitrosylated in the higher nanomolar range and that varying oxygenation of the reaction mixture did not significantly affect the reaction yields. The addition of thiols such as serum albumin (0.6mM), l-cysteine (2.5mM) or N-acetylcysteine (2.5mM) inhibited the NO-MDEA formation indicating that they may prevent N-nitrosamine formation in vivo. However, as S-nitrosothiols may also release NO?, in long term exposure to elevated levels of nitric oxide the nitrosylation of secondary amines may be taken into account.

Detection of bioradicals by in vivo L-band electron spin resonance spectrometry

The applications of in vivo electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscopy have been impressive over a relatively short period despite the many obstacles which had to be overcome, such as dielectric absorption and biodestruction. The loop-gap resonators and modified loop coil systems have emerged as the most suitable resonators for in vivo EPR experiments. This paper briefly discusses instrumental aspects as a prelude to several examples related to the in vivo monitoring and detection of bioradicals. Recent progress in detection of bioradicals induced by drugs or chemicals is discussed with regard to nitrosocompounds, nitric oxide and metals in vivo. A clinical EPR application is also discussed.

A N-Nitrosodimethylamine (NDMA) precursor analysis for chlorination of water and wastewater

N-nitrosodimethylamine (NDMA) is a potent carcinogen formed during chloramination of water and wastewater treatment plant effluents. A procedure is described for quantifying the concentration of the organic precursors of NDMA that could be formed during chlorination of wastewaters and natural waters. The method involves applying a high dose of monochloramine to a pH-buffered sample followed by a 10-day contact period, during which the monochloramine decays at a rate unrelated to the composition of the sample. Analyses of samples of municipal wastewater effluents and surface waters indicate that the method provides a robust and reproducible measurement of NDMA precursors over a wide range of conditions. A sensitive GC/CI/MS/MS analytical procedure for dimethylamine also is described and used to demonstrate that NDMA formation during chlorination of wastewater and natural waters cannot be explained by dimethylamine concentrations alone.

N-nitroso compounds in the gastrointestinal tract of rats and in the feces of mice with induced colitis or fed hot dogs or beef

Because colonic N-nitroso compounds (NOC) may be a cause of colon cancer, we determined total NOC levels by Walters' method in the gastrointestinal tract and feces of rodents: (i) feces of C57BL mice fed chow and semi-purified diets contained 3.2 +/- 0.4 and 0.46 +/- 0.06 NOC/g, respectively (P < 0.01, mean +/- SD). (ii) NOC levels for gastrointestinal contents of three groups of Sprague-Dawley rats fed chow diet were 0.9 +/- 0.05 (diet), 0.2 +/- 0 (stomach), 0.3-0.4 (small intestine), 0.7-1.6 (cecum and colon) and 2.6 +/- 0.6 (feces) nmol/g. NOC precursor (NOCP) levels (measured as NOC after mild nitrosation) for two rat groups fed chow diet showed a 16-fold increase from stomach to proximal small intestine (mean, 6.2 micromol/g), and a 1.7-fold increase from distal colon to feces (mean, 11.6 micromol/g). (iii) Eight Min and five C57BL/6J mice received 4% dextran sulfate sodium in drinking water on days 1-4 to induce acute colitis. This increased fecal NOC levels 1.9-fold on day 5 in both strains (P < or = 0.04), probably due to NO synthase-derived nitrosating agents in the colon. (iv) Following studies on humans fed beef [Hughes et al. (2001) Carcinogenesis, 22, 199], Swiss mice received semi-purified diets mixed with 18% of beef plus pork hot dogs or sautéed beef for 7 days. On day 7, individual 24-h fecal NOC outputs were determined. In three hot dog and two beef groups with 5 mice/group, mean fecal NOC output/day was 3.7-5.0 (hot dog) and 2.0-2.9 (beef) times that for control groups fed semi-purified diet alone (P < 0.002 for each of combined groups). These groups showed little change in fecal NOCP output. (v) Initial purification of rat fecal NOCP by adsorption-desorption and HPLC is described. Results should help evaluate the view that colonic NOC causes colon cancer associated with colitis and ingestion of red and nitrite-preserved meat.

Nitrotyrosine and NO synthases in infants with respiratory failure: influence of inhaled NO

Inhaled nitric oxide (NO) is a selective vasodilator in pulmonary hypertension. However, the safety of inhaled NO (iNO) has not been established. Using an immunohistochemical technique, we studied the expression of NO synthase (NOS) isoforms NOS1, NOS2, NOS3, and nitrotyrosine, the marker of toxic NO-superoxide pathway, in lung specimens from autopsies. Twelve infants dying with respiratory failure had iNO up to 60 parts per million for 0.1-15 days. Twelve control infants were matched in pairs on the basis of the diagnosis, number of gestational days at birth, age at death, and whether extracorporeal perfusion was required. In addition, 5 infants who died of SIDS or nonpulmonary trauma (healthy lungs) were compared to 8 age-matched cases with respiratory failure. Immunostaining was graded by the intensity of the color deposit and the frequency in specific cells stained. Inhaled NO tended to increase NOS2 expression in bronchiolar epithelium and adjacent tissue. There were no other differences in the distribution of nitrotyrosine or NOS isoforms between iNO-treated infants and the control group with respiratory failure. All NOS isoforms were evident in the lungs studied. In severe respiratory failure, nitrotyrosine was mostly detectable in the bronchiolar epithelium and alveolar exudates, whereas in healthy lungs those sites did not contain nitrotyrosine. The alveolar tissue of infants with progressive respiratory may be affected by the NO-superoxide pathway. However, inhalation of NO was not associated with a detectable increase in oxidant stress.

N-nitroso compounds and mutagens in Chinese fermented (sour) corn pancakes

Stomach cancer rates in rural Linqu County, Shandong Province, China, are exceptionally high. A previous case-control study revealed that the risk of stomach cancer was 30% higher among those who consumed sour (fermented) corn pancakes at least daily. A previous study of the sour pancakes reported volatile nitrosamines in most specimens, and almost half reportedly showed mutagenic activity. Few households currently consume sour pancakes, and the duration of fermentation has been shortened. We tested specimens of pancake batter and sour pancakes from Linqu County for mutagenic activity using the Ames test; for N-nitroso compounds (NOC) we used the Nitrolite-thermal energy analysis (TEA) method. Results of the Ames test were inconclusive: only 1 out of 15 cooked pancakes showed a positive mutagenic response, and all 15 batter specimens were negative; however, several batter specimens showed a weakly positive trend of mutagenicity with extract concentration. Our assay for total nitroso compounds was weakly positive in only 1 out of 15 specimens of sour pancake batter. That specimen was also tested by gas chromatography-TEA for nitrosaminoacids and volatile nitrosamines, but none were detected. It seems unlikely that the Chinese sour pancakes are significantly contaminated by NOC or other mutagens.

O6-alkylguanines, dietary N-nitroso compounds, and their precursors in gastric cancer

Several N-nitroso compounds, present in foods and beverages or formed in the stomach from their precursors, act as alkylating agents. By using a highly reliable technique (high-resolution gas chromatography-mass spectrometry with negative-ion chemical ionization and selected ion recording), we measured a series of specific O6-alkylguanines in snap-frozen paired stomach tissue samples (tumor and noninvolved mucosa) obtained at surgery from 24 gastric cancer patients identified in Florence, Italy. Samples of noninvolved mucosa had higher levels of total O6-alkylguanines and more frequently detectable levels (54%) than tumor samples (29.2%). O6-propylguanine and O6-methylguanine were the single adducts most frequently detected in noninvolved mucosa and tumor tissue, respectively. Tumor samples showed higher levels of total O6-alkylguanines in female patients (p = 0.03) and among those with a diffuse histological type (p = 0.06) or seronegative for Helicobacter pylori CagA antibodies (p = 0.06). Mean dietary nitrate intake was significantly higher in patients with detectable levels of adducts in tumor samples (p = 0.03). Estimated intakes of dimethylamine and N-nitrosodimethylamine correlated with total levels of O6-alkylguanines in noninvolved gastric mucosa. These findings, although based on a small series of cases, support a role for N-nitroso compounds from dietary sources in the etiology of gastric cancer.

Formation of N-nitrosodimethylamine (NDMA) from dimethylamine during chlorination

Chlorine disinfection of secondary wastewater effluent and drinking water can result in the production of the potent carcinogen N-nitrosodimethylamine (NDMA) at concentrations of approximately 100 and 10 parts per trillion (ng/L), respectively. Laboratory experiments with potential NDMA precursors indicate that NDMA formation can form during the chlorination of dimethylamine and other secondary amines. The formation of NDMA during chlorination may involve the slow formation of 1,1-dimethylhydrazine by the reaction of monochloramine and dimethylamine followed by its rapid oxidation to NDMA and other products including dimethylcyanamide and dimethylformamide. Other pathways also lead to NDMA formation during chlorination such as the reaction of sodium hypochlorite with dimethylamine. However, the rate of NDMA formation is approximately an order of magnitude slower than that observed when monochloramine reacts with dimethylamine. The reaction exhibits a strong pH dependence due to competing reactions. It may be possible to reduce NDMA formation during chlorination by removing ammonia prior to chlorination, by breakpoint chlorination, or by avoidance of the use of monochloramine for drinking water disinfection.

A kinetic model of N-nitrosodimethylamine (NDMA) formation during water chlorination/chloramination

Experiments were conducted to investigate the hypothesis that N-nitrosodimethylamine (NDMA) is a potential disinfection by-product. NDMA was formed by the reaction of dimethylamine (DMA) with monochloramine and also with free chlorine in the presence of ammonia. We proposed a mechanism for NDMA formation which does not require the presence of nitrite as in N-nitrosation. The critical NDMA formation reactions consist of i) the formation of monochloramine by combination of free chlorine with ammonia, ii) the formation of 1,1-dimethylhydrazine (UDMH) intermediate from the reaction of DMA with monochloramine followed by, iii) the oxidation of UDMH by monochloramine to NDMA, and iv) the reversible chlorine transfer reaction between free chlorine/monochloramine and DMA which is parallel with i) and ii). A kinetic model was developed to validate the proposed mechanism.

Determination of total N-nitroso compounds and their precursors in frankfurters, fresh meat, dried salted fish, sauces, tobacco, and tobacco smoke particulates

Total N-nitroso compounds (NOC) and NOC precursors (NOCP) were determined in extracts of food and tobacco products. Following Walters' method, NOC were decomposed to NO with refluxing HBr/HCl/HOAc/EtOAc and NO was measured by chemiluminescence. NOC were determined after sulfamic acid treatment to destroy nitrite, and NOCP were determined after treatment with 110 mM nitrite and then sulfamic acid. Analysis without HBr gave results < or =20% of those with HBr. This NOC method was efficient for nitrosamines but not nitrosoureas. The standard nitrosation for determining NOCP gave high yields for readily nitrosated amines, including 1-deoxy-1-fructosylvaline, but not for simple amines, dipeptides, and alkylureas. Mean NOC and NOCP results were (respectively, in micromol/kg of product) 5.5 and 2700 for frankfurters, 0.5 and 660 for fresh meat, 5.8 and 5800 for salted, dried fish, and 660 and 2900 for chewing tobacco (all for aqueous extracts) and 220 and 20000 nmol/cigarette for MeCN extracts of cigarette smoke filter pads.

Artifactual-free analysis of S-nitrosoglutathione and S-nitroglutathione by neutral-pH, anion-pairing, high-performance liquid chromatography. Study on peroxynitrite-mediated S-nitration of glutathione to S-nitroglutathione under physiological conditions

The endogenous potent vasodilators and inhibitors of platelet aggregation S-nitrosoglutathione (GSNO) and S-nitroglutathione (GSNO2) are frequently analyzed by high-performance liquid chromatography (HPLC) using mobile phases of acidic pH. These systems are associated with problems stemming from rapid and considerable artifactual formation of GSNO from glutathione (GSH) and ubiquitous nitrite. We describe a novel ion-pairing HPLC method with UV absorbance detection at 334 nm for the highly specific and interference-free analysis of GSNO and GSNO2 in the presence of high GSH and nitrite concentrations. Complete avoidance of artifactual formation of GSNO was accomplished by using the anion-pairing agent tetrabutylammoniumhydrogen sulphate in the mobile phase that enables analysis of GSNO at neutral pH, at which GSH and nitrite do not react to form GSNO. This HPLC system was used to study formation of GSNO2 from GSH and peroxynitrite under physiological conditions. We found by this HPLC system that peroxynitrite (0-300 microM) reacts with GSH (0-5 mM) to form GSNO2 at a mean yield of 2%. Analysis of the same samples by a cation-pairing HPLC system with acidic mobile phase (pH 2.0) revealed, however, GSNO plus GSNO2 formation of the order of 20% due to on column reaction of GSH with peroxynitrite-derived nitrite to form GSNO. Ammonium sulfamate is frequently used to remove nitrite from thiol-containing solutions under acidic conditions. By means of the anion-pairing HPLC system it is demonstrated that nitrite removal by this method is incomplete even when ammonium sulfamate is used at high concentrations. These findings underscore the absolute requirement of neutral pH conditions for the analysis of GSNO. The novel anion-pairing HPLC method should be useful to provide reliable data on formation, reaction and metabolism of GSNO and GSNO2 in biological fluids using various detectors including mass spectrometers.

Electrochemical methods for monitoring of environmental carcinogens

The use of modern electroanalytical techniques, namely differential pulse polarography, differential pulse voltammetry on hanging mercury drop electrode or carbon paste electrode, adsorptive stripping voltammetry and high performance liquid chromatography with electrochemical detection for the determination of trace amounts of carcinogenic N-nitroso compounds, azo compounds, heterocyclic compounds, nitrated polycyclic aromatic hydrocarbons and aromatic and heterocyclic amines is discussed. Scope and limitations of these methods are described and some practical applications based on their combination with liquid-liquid or solid phase extraction are given.

Increased nitrosothiols in exhaled breath condensate in inflammatory airway diseases

Nitrosothiols (RS-NOs) are formed by interaction of nitric oxide (NO) with glutathione and may limit the detrimental effect of NO. Because NO generation is increased in airway inflammation, we have measured RS-NOs in exhaled breath condensate in patients with asthma, cystic fibrosis, or chronic obstructive pulmonary disease (COPD). We also measured exhaled NO and nitrite (NO(2-)) in the same subjects. RS-NOs were detectable in exhaled breath condensate of all subjects. RS-NOs were higher in subjects with severe asthma (0.81 +/- 0.06 microM) when compared with normal control subjects (0.11 +/- 0.02 microM, p < 0.01) and with subjects with mild asthma (0.08 +/- 0.01 microM, p < 0.01). Elevated RS-NOs values were also found in patients with cystic fibrosis (0.35 +/- 0.07 microM, p < 0.01), in those with COPD (0.24 +/- 0.04 microM, p < 0.01) and in smokers (0.46 +/- 0.09 microM, p < 0.01). In current smokers there was a correlation (r = 0.8, p < 0.05) between RS-NOs values and smoking history (pack/year). We also found elevated concentrations of NO(2-) in patients with severe asthma, cystic fibrosis, or COPD, but not in smokers or patients with mild asthma. This suggests that exhaled NO(2-) is less sensitive than exhaled RS-NOs. This study has shown that RS-NOs are detectable in exhaled breath condensate of healthy subjects and are increased in patients with inflammatory airway diseases. As RS-NOs concentrations in exhaled breath condensate vary in the different airway diseases and increase with the severity of asthma, their measurement may have clinical relevance as a noninvasive biomarker of nitrosative stress.

Univariate and simplex optimization for the flow-injection spectrophotometric determination of copper using nitroso-R salt as a complexing agent

A simple colorimetric flow-injection system for the determination of Cu(II) based on a complexation reaction with nitroso-R salt is described. The chemical and FIA variables were established using the univariate and simplex methods. A small volume of Cu(II) was mixed with merged streams of nitroso-R salt and acetate buffer solutions. The absorbance of the complex was continuously monitored at 492 nm. The calibration curve over the concentration range 1.0-7.0 microg ml(-1) was obtained. The relative standard deviation for determining 4.0 microg ml(-1) Cu(II) was 0.47% (n = 11). The detection limit (3sigma) was 0.68 microg ml(-1) and the sample throughput was 150 h(-1). The validity of the method has been satisfactorily examined for the determination of Cu(II) in wastewater and copper ore samples. The accuracy was found to be high, because the student t-values were calculated to be less than the theoretical values when the results were compared with those obtained by FAAS.