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PubMed1977

Effects of amyl nitrite on phasic aortocoronary bypass graft blood velocity in man.

With the use of a Doppler flowmeter catheter, phasic instantaneous aortocoronary saphenous vein bypass graft blood velocity was continuously measured during the inhalation of amyl nitrite in 20 closed-chest conscious subjects. Administration of amyl nitrite augmented peak diastolic and systolic graft blood velocity within 10 seconds and maximal blood velocities were recorded between 8 and 60 seconds after inhalation. Control mean (+/- 1 S.D.) bypass graft blood velocity was 25 +/- 10 cm. per second and after amyl nitrite 46 +/- 14 cm. per second, resulting in an average 84 per cent rise of blood velocity. It is concluded that amyl nitrite increases aortocoronary bypass graft blood velocity, suggesting a possible enhancement of blood flow to the distal native circulation in patients so operated upon.

Adult↗
PubMed1995

Provocation of latent left ventricular outflow tract gradients with amyl nitrite and exercise in hypertrophic cardiomyopathy.

Amyl nitrite may be used to provoke latent gradients in patients with hypertrophic cardiomyopathy (HC) without significant resting outflow tract gradients, but afterload reduction may not be comparable to a more physiologic stressor such as symptom-limited exercise testing. This study compared the ability of amyl nitrite and exercise testing to provoke outflow tract gradients in 57 patients (40 men and 17 women, mean age +/- SD 49 +/- 16 years) with HC (septal thickness 19 +/- 5 mm, average resting gradient 13 +/- 10 mm Hg) who underwent echocardiography at rest, after amyl nitrite inhalation, and after maximal exercise. No significant gradient (< 50 mm Hg) was induced after either provocation in 26 patients (46%); in 15 patients (26%), inducibility was achieved after both stressors, in 6 (11%) after exercise only, and in 10 (18%) after amyl only. Patients with amyl-induced gradients differed from those in whom gradients were noninducible on the basis of smaller outflow tract dimensions (p < 0.001), larger resting gradients (p < 0.001), and a greater prevalence of "septal bulge" morphology (p = 0.02). Those with exercise-induced gradients were able to attain a greater workload (p = 0.07), have larger resting gradients (p = 0.02), and also tended to have a septal bulge morphology (p < or = 0.01). Although outflow tract obstruction increased to similar levels after amyl nitrite (49 +/- 39 mm Hg) and symptom-limited exercise (47 +/- 39 mm Hg), gradients induced by exercise and amyl correlated poorly (r = 0.54).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1991

Kinetics of the reactions of trioxodinitrate and nitrite ions with cytochrome d in Escherichia coli.

The rate of reaction of trioxodinitrate with reduced cytochrome oxidase d in membrane particles from Escherichia coli at pH 7 and 25 degrees C depends linearly upon [HN2O3-] over the concentration range studied (up to 0.05 mM) and is also first-order in cytochrome d. The known rate of decomposition of trioxodinitrate to give NO- and NO2- is about 4.5-times faster than the rate of reaction of reduced cytochrome d with trioxodinitrate, implying that cytochrome d reacts directly with NO-, with a trapping ratio of between 0.20 and 0.25, rather than with trioxodinitrate. The implications of the facile formation of the NO(-)-nitrosyl complex of cytochrome d for the mechanism of denitrification are discussed with particular reference to the mechanism of N-N bond formation. The reaction of reduced cytochrome d with nitrite (a decomposition product of trioxodinitrate) under these conditions is much slower than that with trioxodinitrate. The kinetics show a biphasic dependence of initial rate upon nitrite concentration. The rate data at low [NO2-] are consistent with saturation of a high affinity site for nitrite, having Vmax = 4.29.10(-9) M s-1 and Km = 0.034 mM. The existence of two binding sites for nitrite is consistent with the suggestion that the cytochrome bd complex contains two cytochrome d haems.

Cytochrome d Group↗
PubMed1999

Membrane effects of nitrite-induced oxidation of human red blood cells.

The aim of our investigation was to study the red blood cell (RBC) membrane effects of NaNO(2)-induced oxidative stress. Hyperpolarization of erythrocyte membranes and an increase in membrane rigidity have been shown as a result of RBC oxidation by sodium nitrite. These membrane changes preceded reduced glutathione depletion and were observed simultaneously with methemoglobin (metHb) formation. Changes of the glutathione pool (total and reduced glutathione, and mixed protein-glutathione disulfides) during nitrite-induced erythrocyte oxidation have been demonstrated. The rates of intracellular oxyhemoglobin and GSH oxidation highly increased as pH decreased in the range of 7.5-6.5. The activation energy of intracellular metHb formation obtained from the temperature dependence of the rate of HbO(2) oxidation in RBC was equal to 16.7+/-1.6 kJ/mol in comparison with 12.8+/-1.5 kJ/mol calculated for metHb formation in hemolysates. It was found that anion exchange protein (band 3 protein) of the erythrocyte membrane does not participate significantly in the transport of nitrite ions into the erythrocytes as band 3 inhibitors (DIDS, SITS) did not decrease the intracellular HbO(2) oxidation by extracellular nitrite.

Benzothiazoles↗
PubMed2003

Crystal structure of a NO-forming nitrite reductase mutant: an analog of a transition state in enzymatic reaction.

I257E was obtained by site directed mutagenesis of nitrite reductase from Achromobacter cycloclastes. The mutant has no enzyme activity. Its crystal structure determined at 1.65A resolution shows that the side-chain carboxyl group of the mutated residue, Glu257, coordinates with the type 2 copper in the mutant and blocks the contact between the type 2 copper and its solvent channel, indicating that the accessibility of the type 2 copper is essential for maintaining the activity of nitrite reductase. The carboxylate is an analog of the substrate, nitrite, but the distances between the type 2 copper and the two oxygen atoms of the side-chain carboxyl group are reversed in comparison to the binding of nitrite to the native enzyme. In the mutant, both the type 2 copper and the N epsilon atom on the imidazole ring of its coordinated residue His135 move in the substrate binding direction relative to the native enzyme. In addition, an EPR study showed that the type 2 copper in the mutant is in a reduced state. We propose that mutant I257E is in a state corresponding to a transition state in the enzymatic reaction.

Alcaligenes↗
PubMed1992

Low density lipoprotein inhibits accumulation of nitrites in murine brain endothelial cell cultures.

Endothelial cells produce nitric oxide which is considered to serve as a major source of endothelial derived relaxing factor activity. It has been demonstrated that activation of mouse brain endothelium by TNF-alpha and IFN-gamma led to accumulation of nitrite which is presumably formed by oxidation of nitric oxide. A number of studies suggest that reactive oxygen species produced by cytokine-activated cells are involved in the conversion of nitric oxide to nitrites and nitrates. We investigated whether low density lipoprotein (LDL), acting as a radical scavenger, is able to inhibit nitrite accumulation in mouse brain endothelial cell cultures and in a cell-free system in which sodium nitroprusside was used as a source of nitric oxide. A comparison of these two models indicates the active involvement of LDL in suppressing nitrite accumulation in murine endothelial cultures.

Animals↗
PubMed1997

Interleukin-6 increases the levels of cyclic GMP and nitrite in rat hippocampal slices.

We examined the effect of interleukin-6 on the levels of cGMP and nitrite in rat hippocampal slices. Interleukin-6 at 400 ng/ml time dependently increased the content of cGMP of slices after incubation for 1, 2, 3, and 4 h, and the effect of interleukin-6 was maximal at 2 h post-incubation. In addition, exposure of slices to interleukin-6 at 80, 400 and 2000 ng/ml or at 16, 80 and 400 ng/ml for 2 h significantly elevated the cGMP level and nitrite level, respectively, in a concentration-dependent manner. Also, 0.1 mM NG-nitro-L-arginine alone showed no effect on either the cGMP level or the nitrite level. However when incubated in conjunction with 400 ng/ml interleukin-6 for 2 h, NG-nitro-L-arginine apparently prevented the increase in cGMP and nitrite induced by 400 ng/ml interleukin-6. The present results show that NO mediates the increase in cGMP induced by interleukin-6 and suggest that interleukin-6 may exert an inducible effect on the NO synthase in hippocampal slices.

Animals↗
PubMed2002

Modification of heme c binding motifs in the small subunit (NrfH) of the Wolinella succinogenes cytochrome c nitrite reductase complex.

The two multiheme c-type cytochromes NrfH and NrfA form a membrane-bound complex that catalyzes menaquinol oxidation by nitrite during respiratory nitrite ammonification of Wolinella succinogenes. Each cysteine residue of the four NrfH heme c binding motifs was individually replaced by serine. Of the resulting eight W. succinogenes mutants, only one is able to grow by nitrite respiration although its electron transport activity from formate to nitrite is decreased. NrfH from this mutant was shown by matrix-assisted laser desorption/ionization mass spectrometry to carry four covalently bound heme groups like wild-type NrfH indicating that the cytochrome c biogenesis system II organism W. succinogenes is able to attach heme to an SXXCH motif.

Amino Acid Motifs↗
PubMed2004

Peroxynitrite formation from the simultaneous reduction of nitrite and oxygen by xanthine oxidase.

One electron reductions of oxygen and nitrite by xanthine oxidase form peroxynitrite. The nitrite and oxygen reducing activities of xanthine oxidase are regulated by oxygen with K(oxygen) 26 and 100 microM and K(nitrite) 1.0 and 1.1 mM with xanthine and NADH as donor substrates. Optimal peroxynitrite formation occurs at 70 microM oxygen with purine substrates. Kinetic parameters: V(max) approximately 50 nmol/min/mg and K(m) of 22, 36 and 70 microM for hypoxanthine, pterin and nitrite respectively. Peroxynitrite generation is inhibited by allopurinol, superoxide dismutase and diphenylene iodonium. A role for this enzyme activity can be found in the antibacterial activity of milk and circulating xanthine oxidase activity.

Animals↗
PubMed1999

Nitrite reductase activity is a novel function of mammalian mitochondria.

Nitrite, which is the major stable degradation product of nitric oxide, exists in all tissues capable of nitric oxide synthesis from L-arginine. The present study provides experimental evidence that nitrite in contact with respiring mitochondria accepts reducing equivalents from the ubiquinone cycle of the respiratory chain. Univalent reduction of nitrite was totally inhibited by myxothiazol. We therefore conclude on the involvement of redox cycling that ubisemiquinone is associated with the bc1 complex. Recycling of nitric oxide degradation products via these electron carriers may become a threat to energy-linked respiration since nitric oxide in direct contact with mitochondria was shown to slow the energy-linked respiration down and to trigger a mitochondrial source for superoxide radicals. Until now, the existence of nitrite reductase activity was only demonstrated in plants and bacteria. In addition, the present observation elucidates the existence of a nitric oxide synthase-independent nitric oxide source.

Animals↗
PubMed1981

Determination of nitrite in human, cow and market milks by gas-liquid chromatography with electron-capture detection.

A simple and practical method for the determination of very small amounts of nitrite in human, cow and market milks is described. It is based on the reaction of nitrate with 1-hydrazinophthalazine in acidic solution to form tetrazolophthalazine, a stable compound which can be extracted with an organic solvent and then determined by gas-liquid chromatography with electron-capture detection using a column of 3% OV-225 on Chromosorb W HP; the detection limit for nitrite was 2 ng/ml. The procedure for determining nitrite in milks involves extraction with solvent, followed by further clean-up by alumina column chromatography; the detection limit is about 4 ppb and recovery in human, cow and market milks was satisfactory. The method makes possible a micro-assay for nitrite. The tetrazolophthalazine was identified by its elemental composition, melting point and by combined gas chromatography-mass spectrometry.

Animals↗
PubMed2003

Ion chromatographic method for the simultaneous determination of nitrite and nitrate by post-column indirect fluorescence detection.

This short paper highlights the suitability of ion chromatography with post-column indirect fluorescence detection to determine simultaneously nitrite and nitrate based on the quenching of tryptophan native fluorescence. The method uses an enhanced fluorescence mobile phase containing tryptophan and detects the suppression of fluorescence of the mobile phase due to the elution of the target ions. The phenomenon of fluorescence quenching of tryptophan is highly induced by the presence of phosphate ions. The quenched fluorescence intensity exhibits concentration dependence in the range 1-25 mg/l and 3-65 mg/l for nitrite and nitrate, respectively. The relative standard deviation for five replicates of a standard solution containing a mixture of 5 mg/l of nitrite and 10 mg/l of nitrate lies around 2.8%. This simple coupling technique results in a relatively sensitive, fast, and accurate method, allowing for both qualitative and quantitative analysis of nitrite and nitrate. The method can easily be implemented to real samples such as foodstuffs, fertilizers and soils and is proven to be precise and accurate when compared with reference methods.

Chromatography, Liquid↗
PubMed2003

Development of a novel running buffer for the simultaneous determination of nitrate and nitrite in human serum by capillary zone electrophoresis.

In order to improve NO2- peak height and obtain a convenient buffer system for the assay of nitrogen monooxide metabolites, we developed a novel running buffer for the simultaneous determination of nitrite and nitrate in human serum by capillary electrophoresis. The addition of cetyltrimethylammonium chloride to the running buffer resulted in high-speed separation using reverse electroosmotic flow. Highly sensitive determination was also achieved using stacking with 10-fold diluted sample solutions. The samples were injected hydrodynamically for 100 s into a 50 cm x 75 microm I.D. capillary. The separation voltage was 10 kV (negative polarity). UV detection was performed at 214 nm. We obtained complete separation of nitrite and nitrate in deproteinized human serum within 6 min with optimum analytical conditions. Linear calibration curves for nitrite and nitrate for both peak height and peak area were obtained with standard addition method. The limits of detection obtained at a signal-to-noise ratio of 3 for nitrite and nitrate were 4.1 and 2.0 microM, while the values of relative standard deviation of peak height were 2.4 and 2.6%, respectively.

Buffers↗
PubMed1996

Increased urinary nitrite excretion in children with minimal change nephrotic syndrome.

OBJECTIVE: We tested the hypothesis that nitric oxide synthesis by the kidney is increased in children with primary nephrotic syndrome. METHODS: We examined the urinary excretion of nitrite, a stable metabolite of nitric oxide, using the Griess reaction, in children with nephrotic syndrome. RESULTS: In comparison with healthy children, patients with minimal change nephrotic syndrome had increased urinary nitrite excretion regardless of whether the disease was in relapse or remission (p < 0.025). In contrast, urinary nitrite excretion was similar in control subjects and patients with focal segmental glomerulosclerosis or IgA nephropathy. CONCLUSION: These findings indicate that measurement of urinary nitrite excretion may be a useful test to help discriminate between minimal change nephrotic syndrome and focal segmental glomerulosclerosis in children with idiopathic nephrotic syndrome.

Adolescent↗
PubMed1998

Elevated cerebrospinal fluid and serum nitrate and nitrite levels in patients with central nervous system complications of HIV-1 infection: a correlation with blood-brain-barrier dysfunction.

As nitric oxide (.NO) is hypothesised to play a role in the immunopathogenesis of neurological complications associated with inflammation, we compared levels of cerebrospinal fluid (CSF) and serum .NO metabolites in 24 patients with HIV-1 infection, to those in 58 non-HIV infected patients with neurological disorders. Levels of .NO metabolites were correlated with blood-brain-barrier dysfunction. CSF and serum nitrate and nitrite levels were measured by the nitrate reductase and Griess reaction methods. The .NO metabolites, nitrate and nitrite, were raised in the CSF and serum of patients with AIDS and central nervous system complications, when compared to non-HIV infected patients with inflammatory and non-inflammatory neurological disorders (median nitrate and nitrite: CSF=18.3 microM vs. 11.1 microM vs. 7.0 microM, P<0.001, and serum=53.8 microM vs. 50.3 microM vs. 41.4 microM, P=0.04, respectively). CSF nitrate and nitrite levels correlated with the albumin quotient. This study supports the evidence that .NO is a potential mediator of blood-brain-barrier breakdown in inflammatory diseases of the central nervous system.

Acquired Immunodeficiency Syndrome↗
PubMed1976

Gastric-juice nitrite. A risk factor for cancer in the hypochlorhydric stomach?

Nitrite and hydrogen ion concentrations have been measured in the fasting gastric juice of 69 patients undergoing routine gastrointestinal investigations. There was an inverse relationship between nitrite concentration and hydrogen ion concentration, with a highly significant increase in gastric-juice nitrite in hypochlorhydric subjects. Thiocyanate was also found in all specimens in concentrations likely to increase nitrosamine formation, if nitrosation of amines occurs in the fasting stomach. Neutral gastric juice contains metabolically active bacteria capable both of generating nitrite from nitrate and of catalysing nitrosation. In this way an intragastric environment suitable for the formation of carcinogenic nitrosamines exists in the hypochlorhydric and achlorhydric stomach, providing a possible mechanism for the high incidence of gastric cancer in these subjects.

Achlorhydria↗
PubMed2001

Can voltammetry measure nitrogen monoxide (NO) and/or nitrites?

Recently, voltammetry with carbon fibre electrodes (CFE) has been implemented for real time measurement of nitrogen monoxide (NO) indicating that it is oxidised at the potential value of nitrites, approximately +700 mV. In contrast, here we show that modified CFE can monitor NO at oxidation potentials different than that of nitrites, i.e. +550 mV. Indeed, at +550 mV a significant increase of amperometric current levels was obtained when NO but not nitrites, were added to a phosphate buffer saline solution (PBS). Differential pulse voltammetry (DPV) supports these findings as two oxidation peaks were obtained when examining air preserved NO; peak 1 at +550 mV and peak 2 at +700 mV, respectively. In contrast, only peak 2 was monitored when nitrites or a solution of NO oxidised in air was added to PBS. Biological support to these in vitro data comes from the observation that the relaxation of an adrenaline-contracted aortic ring produced via addition of NO is concomitant with peak 1 at +550 mV. The relaxation is almost completed before the appearance of peak 2 at +700 mV. Furthermore, in vivo experiments performed in the striatum of rats show that the amperometric signal monitored at +550 mV is responsive to glutamatergic stimulation or inhibition of NO synthase.

2-Amino-5-phosphonovalerate↗
PubMed1998

Immunomodulation by nitrite inhalants may predispose abusers to AIDS and Kaposi's sarcoma.

Epidemiological studies indicating that nitrite inhalant abuse is a co-factor in HIV infection and in Kaposi's sarcoma are supported by recent experimental studies, described in this review. Inhalation exposure to the nitrites produce a nonspecific cytotoxicity, depleting many cells of the immune system. Apparently distinct from this cytotoxicity, inhalation of the nitrites impairs a variety of immune mechanisms, affecting both humoral and cell-mediated immunity. In addition, the inhalant-increased macrophage production of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), can directly stimulate HIV replication and can also stimulate the growth of Kaposi's sarcoma cells. Thus, nitrite inhalants may impair immune resistance to infection and actively promote viral replication and tumor growth.

Acquired Immunodeficiency Syndrome↗