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PubMed1975

Correction for spectral interference with determination of lead in blood by non-flame atomic absorption spectrometry.

A non-flame atomizer incorporating a graphite tube and cup is used to determine lead in whole blood and packed erythrocytes. In a direct method, a 2-mu-l sample is treated in situ in the cup with 1 mu-l of concentrated nitric acid. The oxidized sample can then be dried, ashed, and atomized without leaving a residue. The nitric acid treatment obviates correction for nonselective absorption, something previously necessary in the determination of lead in blood by non-flame techniques. The resulting chemical conversion of the matrix compounds frees the lead atomic absorption peak from the spectral interference. Alternatively, a 50-mu-l sample of blood or erythrocytes is treated with 50 mu-l of concentrated nitric acid and a 1.5-mu-l aliquot is analyzed with use of the graphite tube.

Erythrocytes↗
PubMed2003

Effect of tumor necrosis factor-alpha on endothelial and inducible nitric oxide synthase messenger ribonucleic acid expression and nitric oxide synthesis in ischemic and nonischemic isolated rat heart.

OBJECTIVES: The present study aimed to investigate the influence of endogenous tumor necrosis factor-alpha (TNF-alpha) that was synthesized during ischemia and exogenous TNF-alpha on endothelial and inducible nitric oxide synthase (eNOS and iNOS) messenger ribonucleic acid (mRNA) expression and nitric oxide (NO) production in the isolated rat heart. BACKGROUND: Tumor necrosis factor-alpha is recognized as being a proinflammatory cytokine with a significant cardiodepressant effect. One of the proposed mechanisms for TNF-alpha-induced cardiac contractile dysfunction is increased NO production via iNOS mRNA upregulation, but the role of NO in TNF-alpha-induced myocardial dysfunction is highly controversial. METHODS: Isolated rat hearts studied by a modified Langendorff model were randomly divided into subgroups to investigate the effect of 1-h global cardioplegic ischemia or the effect of 1-h perfusion with exogenous TNF-alpha on the expression of eNOS mRNA and iNOS mRNA and on NO production. RESULTS: After 1 h of ischemia, there were significant increases in TNF levels in the effluent (from hearts), and eNOS mRNA expression had declined (from 0.91 +/- 0.08 to 0.68 +/- 0.19, p < 0.001); but there were no changes in iNOS mRNA expression, and NO was below detectable levels. Perfusion of isolated hearts with TNF-alpha had a cardiodepressant effect and decreased eNOS mRNA expression to 0.67 +/- 0.04 (p < 0.002). Inducible nitric oxide synthase mRNA was unchanged, and NO was below detectable levels. CONCLUSIONS: We believe this is the first study to directly show that TNF-alpha does not increase NO synthesis and release but does downregulate eNOS mRNA in the ischemic and nonischemic isolated rat heart.

Animals↗
PubMed2002

Oxidation of quercetin by salivary components. Quercetin-dependent reduction of salivary nitrite under acidic conditions producing nitric oxide.

Under acidic conditions, nitrite is protonated to nitrous acid (pK(a) = 3.2-3.4) that can be transformed into nitric oxide by self-decomposition and reduction. When sodium nitrite was mixed with quercetin at pH 1-2, quercetin was oxidized producing nitric oxide. In addition to quercetin, kaempferol and quercetin 4'-glucoside were also oxidized by nitrous acid, but oxidation of apigenin, luteolin, and rutin was slow compared to oxidation of the above flavonols. These results suggested that flavonols, which have a free hydroxyl group at carbon position 3, can readily reduce nitrous acid to nitric oxide. When the pH of saliva was decreased to 1-2, formation of nitric oxide was observed. The nitric oxide formation was enhanced by quercetin, and during this process quercetin was oxidized. These results indicate that there is a possibility of reactions between phenolics and nitrous acid derived from salivary nitrite in the stomach.

Flavonoids↗
PubMed2003

Study of extraction conditions for the quantitative determination of Hg bound to sulfide in soils from Almaden (Spain).

Almaden mine (Spain) is the largest source of cinnabar (HgS) in the world. The purpose of this study is to evaluate, compare and optimize the analytical conditions for the quantitative determination of Hg bound to sulfide in soil samples from mining area of Almaden. A sequential extraction procedure was performed in two stages. The first one was based on a nitric acid leaching. An optimization of certain extraction conditions in this stage was carried out. In order to assess the suitability of the nitric acid leaching, an additional study of possible interfering compounds that might promote the solubility of HgS in nitric acid was developed. The quantitative determination of Hg bound to sulfide was considered in a second stage. A comparative study was carried out among three different procedures: i) extraction with a saturated Na(2)S solution from the residue remaining in the first stage, ii) microwave assisted dissolution of the remaining Hg in this residue with aqua regia, and iii) quantification by difference between total Hg content and Hg extracted in the first stage. The recoveries of Hg bound to sulfide were found to be comparable for the three proposed procedures. Soil samples coming from Almaden mining area were analysed by this method. The distribution of Hg chemical forms was found to be similar for the two parcels tested, and the recoveries of bound to sulfide Hg ranged from 83% to 96% of total Hg content.

Journal Article↗
PubMed2004

Simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by slurry-sampling graphite furnace AAS.

A fast and accurate analytical method was established for the simultaneous direct determination of aluminum, calcium and iron in silicon carbide and silicon nitride powders by graphite furnace atomic absorption spectrometry using a slurry sampling technique and a Hitachi Model Z-9000 atomic absorption spectrometer. The slurry samples were prepared by the ultrasonication of silicon carbide or silicon nitride powders with 0.1 M nitric acid. Calibration curves were prepared by using a mixed standard solution containing aluminum, calcium, iron and 0.1 M nitric acid. The analytical results of the proposed method for aluminum, calcium and iron in silicon carbide and silicon nitride reference materials were in good agreement with the reference values. The detection limits for aluminum, calcium and iron were 0.6 microg/g, 0.15 microg/g and 2.5 microg/g, respectively, in solid samples, when 200 mg of powdered samples were suspended in 20 ml of 0.1 M nitric acid and a 10 microl portion of the slurry sample was then measured. The relative standard deviation of the determination of aluminum, calcium and iron was 5 - 33%.

Journal Article↗
PubMedDate not supplied

Retention of chromium (VI) on a macroporous char following ChemChar gasification and successive leaching with water and acids.

A granular macroporous char, triple-reverse-burn (TRB) char, was loaded with 23.40 mg Cr/g TRB char from an aqueous solution, and the retained metal was leached by water, 0.66 M nitric acid, concentrated nitric acid, and concentrated hydrochloric acid before and after treatment by a reductive thermal gasification process (ChemChar process developed by ChemChar Research, Inc., Columbia, Missouri). The chromium leachate was analyzed by flame atomic adsorption. Reverse- and forward-mode gasifications were performed on the metal-laden char. With the exception of a 10% mass loss of carbon, the reverse mode gasification process does not change the physical characteristics of the granular char, but does increase the retention of the chromium from 16.7 to 24.2%, depending on the leachant. The forward mode gasification process produces a vitrified (or glasslike) ash residue. There was an 11.6 to 13.1% increase in the retention of the chromium by the slag and ash when compared to the nongasified chromium-loaded TRB char. Chromium (VI) was effectively removed from solution by TRB char and found to be retained to a higher degree on the char after a reductive thermal treatment.

Adsorption↗
PubMed1999

Isolation and characterization of diazoate intermediate upon nitrous acid and nitric oxide treatment of 2'-deoxycytidine.

The intermediate produced from dCyd by HNO2 and NO treatments was isolated and characterized. When 10 mM dCyd was treated with 100 mM NaNO2 in 1.0 M acetate buffer (pH 3.7) at 37 degrees C, a previously unidentified product was formed. By spectrometric measurements, the product was identified as a diazoate derivative of dCyd, 1-(beta-D-2'-deoxyribofuranosyl)-2-oxopyrimidine-4-diazoate. The time course of the concentration change of the diazoate showed a profile characteristic of a reaction intermediate, and the maximum yield was 37 microM at the reaction time of 25 min. Up to the reaction time of 10 min, the diazoate concentration was greater than that of dUrd, a deamination product of dCyd. Addition of thiocyanate increased the yield of the diazoate in HNO2 treatment, whereas addition of ascorbate decreased the yield. When 10 mM dCyd in 100 mM phosphate buffer was treated with NO at 37 degrees C under aerobic conditions holding the pH (7.2-7.6), the diazoate was also generated. The yield of the diazoate was higher than that of dUrd up to 15 mmol of NO absorption. At pH 3.7 and 37 degrees C, the diazoate was converted to dUrd with the first-order rate constant k = 4.8 x 10(-)4 s-1 (t1/2 = 24 min). Under physiological conditions (pH 7.4, 37 degrees C), however, it was fairly stable (k = 5.8 x 10(-)7 s-1, t1/2 = 330 h). In both cases, the diazoate was converted to dUrd exclusively and no other intermediates were detected by HPLC analysis. Uracil-DNA glycosylase did not remove the diazoate residue from an oligodeoxynucleotide containing this damage, [d(T6DT5), D = the diazoate]. The Tm value of a duplex containing the diazoate, d(T6DT5).d(A5GA6), was much lower than that of a duplex containing a correct C:G base pair, d(T6CT5).d(A5GA6). These results show that the diazoate is generated as a stable intermediate in the reactions of dCyd with HNO2 and NO and that the major product is the diazoate but not dUrd in the initial stage of the reactions. Thus, once formed in vivo, the diazoate persists for long time in DNA and may act as a major cytotoxic and/or genotoxic lesion with biologically relevant doses of HNO2 and NO.

DNA Glycosylases↗
PubMed1990

Induction of nitroarenes in cigarette smoke condensate treated with nitrate.

Samples of cigarette smoke condensates (CSCs) treated with nitric acid or Chinese cabbage pickles having a high nitrate content strongly mutated Salmonella typhimurium strain TA98; the benzene/ethanol extract after these treatments induced 1800 and 820 revertants, respectively, per mg of extract for strain TA98 in the absence of S9 mix. The major mutagens in these materials were found to be 1-nitropyrene and 1,3-dinitropyrene on the basis of the result of gas chromatography/mass spectrometry and of fluorescence spectra of the samples. The quantity of 1-nitropyrene was 14.5 ng per cigarette for the CSCs treated with nitric acid, and for 11.2 ng for those treated with Chinese cabbage pickles. Similarly, 1,3-dinitropyrene was detected in the CSCs treated with nitric acid or Chinese cabbage pickles at concentrations of 0.38 and approximately 0.1 ng, respectively, per cigarette.

Biotransformation↗
PubMed2006

D-Aspartic acid and nitric oxide as regulators of androgen production in boar testis.

D-Aspartic acid (D-Asp) and nitric oxide (NO) are two biologically active molecules playing important functions as neurotransmitters and neuromodulators of nerve impulse and as regulators of hormone production by endocrine organs. We studied the occurrence of D-Asp and NO as well as their effects on testosterone synthesis in the testis of boar. This model was chosen for our investigations because it contains more Leydig cells than other mammals. Indirect immunofluorescence applied to cryostat sections was used to evaluate the co-localization of D-Asp and of the enzyme nitric oxide synthase (NOS) in the same Leydig cells. D-Asp and NOS often co-existed in the same Leydig cells and were found, separately, in many other testicular cytotypes. D-Asp level was dosed by an enzymatic method performed on boar testis extracts and was 40+/-3.6 nmol/g of fresh tissue. NO measurement was carried out using a biochemical method by NOS activity determination and expressed as quantity of nitrites produced: it was 155.25+/-21.9 nmol/mg of tissue. The effects of the two molecules on steroid hormone production were evaluated by incubating testis homogenates, respectively with or without D-Asp and/or the NO-donor L-arginine (L-Arg). After incubation, the testosterone presence was measured by immunoenzymatic assay (EIA). These in vitro experiments showed that the addition of D-Asp to incubated testicular homogenates significantly increased testosterone concentration, whereas the addition of L-Arg decreased the hormone production. Moreover, the inclusion of L-Arg to an incubation medium of testicular homogenates with added D-Asp, completely inhibited the stimulating effects of this enantiomer. Our results suggest an autocrine action of both D-Asp and NO on the steroidogenetic activity of the Leydig cell.

Animals↗
PubMed2006

Cytosolic calcium microdomains by arachidonic acid and nitric oxide in endothelial cells.

Intracellular calcium signals activated by growth factors in endothelial cells during angiogenesis regulate cytosolic and nuclear events involved in survival, proliferation and motility. Among the intracellular messengers released after proangiogenic stimulation (bFGF, VEGF), arachidonic acid (AA), nitric oxide (NO) and their metabolites play a key role and their effects are strictly related to calcium homeostasis. Recently, we showed that AA and NO are able to stimulate the opening of store-independent calcium-permeable channels in the plasmamembrane of bovine aortic endothelial cells (BAECs). Here, we studied the intracellular spatiotemporal dynamics of AA- and NO-induced calcium increases following store-independent calcium entry from extracellular medium. Using confocal calcium imaging, we show that calcium entry is preferentially restricted to peripheral cytosolic microdomains and does not necessarily invade the nuclear region. These results support the existence of local mitogen-activated calcium signals. Several factors could account for this spatial restriction, including the geometry of the cells and the clusterization of calcium channels and other signalling molecules. Intracellular calcium fingerprints could contribute to the specificity of endothelial cell responses to angiogenic factors.

Animals↗
PubMed2006

[Isoflavone accumulation associated with cell structural changes in Maackia amurensis suspension cultures elicited by methyl jasmonate, salicylic acid and nitric oxide].

Comparison between changes in isoflavone accumulation and cell structure in Maackia amurensis suspension cultures elicited by methyl jasmonate (MeJA),salicylic acid (SA) and nitric oxide (NO) was studied. The results suggested that MeJA, SA and NO can all stimulate isoflavone production remarkably. After 9d treatment with 200 micromol/L MeJA,100 micromol/L SA and 50 micromol/L SNP, the isoflavone content was 417.18%, 185.45% and 222.45% of the control, respectively. At the same time, the electron-dense body (EDB) could be easily found in the cells, while its number achieved most after 9 d treatment,and the number of EDB and isoflavone content were positive correlated. It was deduced that elicitors stimulated plant secondary metabolites production associated with changes in cell structure.

Acetates↗
PubMed1987

Effect of histological decalcifying agents on number and stainability of gram-positive bacteria.

In tests of the effects of restorative materials on dental pulp, it is important that one evaluate bacterial contamination, and this is usually done histologically. Preceding the usual paraffin-embedding of hard-tissue specimens for microscopical investigations, decalcification is performed. To study the influence of decalcifying agents (nitric acid, formic acid, and ethylenediamine tetraacetic acid) on the number and Gram-stainability of bacteria, we used a model system consisting of suspensions of formaldehyde-fixed Streptococcus faecalis. The Gram-positive organisms were stored in distilled water, in 4% formaldehyde solution, or in the decalcifying agents for various experimental periods. Counts were made by means of a hemocytometer, and smears were stained with the Brown and Brenn staining method. After periods which are averages for the decalcification of teeth, severe reductions of both the number and the Gram-positive stainability were found. After one week in formic acid, only one out of 15 organisms stained blue. With nitric acid and EDTA, the reductions were fewer. Since only blue-staining bacteria can be detected clearly in tissue sections, the results of these experiments indicate that, with limited numbers of organisms, the risk exists for false-negative scores for decalcified hard-tissue sections.

Edetic Acid↗
PubMed2003

Quercetin-dependent reduction of salivary nitrite to nitric oxide under acidic conditions and interaction between quercetin and ascorbic acid during the reduction.

A salivary component, nitrate, is reduced to nitrite in the oral cavity. Polyphenols in foods are mixed with nitrite in the saliva to be swallowed into the stomach. An objective of the present study is to elucidate reactions between a polyphenol quercetin and a nitrite under acidic conditions. Nitric oxide, which is formed by the reactions between nitrous acid and quercetin or ascorbic acid (AA), can be measured using an oxygen electrode in the saliva as well as a buffer solution. The initial oxidation of quercetin was inhibited by AA, and quercetin enhanced the oxidation of AA, suggesting AA-dependent reduction of quercetin radicals, which might be formed during the oxidation of quercetin by nitrous acid. On the basis of the above results, the usefulness of an oxygen electrode for the measurement of nitrite-dependent nitric oxide formation under acidic conditions is proposed and the possible mechanism of reduction of nitrous acid by quercetin and the interaction between quercetin and AA, which is a normal component in the gastric juice, for the reduction of nitrous acid is discussed.

Ascorbic Acid↗
PubMed2003

Preliminary study of the stability of calix[4]arene crown compounds under radiolysis.

The extraction of (135)Cs from high activity waste arising from reprocessing of spent fuel can be achieved by using calix[4]arene crown compounds. The radiolytic degradation of calix[4]arene crowns as well as their solvent, o-nitrophenyloctyl ether (NPOE), was studied using electrospray ionization mass spectrometry (ESI-MS) (that formed Cs(+) or Na(+) adducts) in nitric acid, as well as by chemical ionization tandem mass spectrometry (MS/MS) experiments. The structures of major degradation products were identified with MS and specifically labelled nitric acid. Although NPOE and calix[4]arene crowns alone are relatively stable, under simulated conditions resembling the real industrial processes involving radiolysis in the presence of nitric acid, several products resulting from nitration and oxidation were observed.

Journal Article↗
PubMed2005

Ascorbic acid enhances nitric oxide production in trabecular meshwork cells.

PURPOSE: This study investigated the role of ascorbic acid on the production of nitric oxide (NO) in the trabecular meshwork (TM) cells. METHODS: After primarily cultured human TM cells were exposed to 1, 10, and 100 microM of L-ascorbic acid (LAA), with or without co-administration of 1 mM sodium nitroprusside or 100 microM hydrogen peroxide for 48 hr, cellular survival and NO production were measured with MTT and Griess assay, respectively. RESULTS: LAA significantly potentiated NO production in a dose-dependent manner (p<0.05) without affecting cell viability. LAA increased cell viability after hydrogen peroxide-induced oxidative stress in a dose-dependent manner. LAA enhanced NO production in TM cells and showed a cytoprotective effect against hydrogen peroxide-induced oxidative stress. CONCLUSIONS: LAA might be involved in the regulation of trabecular outflow by enhancing NO production in TM cells.

Ascorbic Acid↗