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PubMed1998

Enzymic method for the determination of nitrite in meat and fish products.

A simple spectrophotometric method for the determination of nitrite is described. Nitrite is measured enzymically through its reaction with nitrite reductase coupled with NADH. The entire enzymic procedure required 15 min to complete. The calibration curve was linear in the range 0.1-10 micrograms cm-3 nitrite with a slope of 6.25. The relative standard deviation at 5 microgram g-1 was 1.7% (n = 5). The method greatly simplifies the procedure of nitrite determination and enables the routine inspection of a number of samples with very little laboratory equipment. A comparison study showed that the method was superior to the GC method for samples containing large amounts of reducing substances while good agreement was achieved between both methods for other foods.

Fish Products↗

PubMed1994

Effect of increasing intravesicular pH on nitrite production and leishmanicidal activity of activated macrophages.

We examined the effect of bafilomycin A1 (BAF), an inhibitor of vacuolar-type H(+)-ATPases, on macrophages activation (measured as increased nitrite production and leishmanicidal activity) induced by interferon gamma alone or together with lipopolysaccharide or tumour necrosis factor alpha. BAF increased intravesicular pH and enhanced nitrite release by activated macrophages; however, the NO concentration necessary to kill parasites was higher in BAF-exposed than control macrophages, suggesting that microbicidal nitrogen derivatives were less active at alkaline pH. Antibody to tumour necrosis factor alpha inhibited BAF-induced nitrite production in interferon-activated cultures. To determine if enhanced NO synthesis was related to vesicular alkalinization, macrophages were incubated with the lysosomotropic bases NH4Cl and methylamine. These agents also increased intravesicular pH and nitrite production. Nitrite production was correlated with enhanced NO synthase activity in cytosolic extracts of the activated cells.

Amino Acid Oxidoreductases↗

PubMed2003

Is apoptosis in antral mucosa correlated with serum nitrite concentration in Japanese Helicobacter pylori-infected patients?

BACKGROUND AND AIM: Helicobacter pylori infection in gastric mucosa is a form of chronic active gastritis that leads to expression of inducible nitric oxide synthase in host macrophages and polymorphonuclear leukocytes. Nitric oxide produced by these cells infiltrating the gastric mucosa could damage DNA. We correlated apoptosis in H. pylori-infected antral tissue from peptic ulcer patients with serum nitrate-plus-nitrite. METHODS: Biopsy specimens were obtained endoscopically from antrum and fundus in 17 peptic ulcer patients before and after H. pylori eradication. Tissue samples were subjected to rapid urease testing and histopathological scoring (updated Sydney system), as well as immunohistochemical detection of single-stranded DNA indicating apoptotic cells. Fasting serum samples were analyzed for combined nitrate and nitrite content. RESULTS: In all cases atrophy was absent to mild in antral mucosa and H. pylori was eradicated successfully. A strong positive correlation was present between apoptosis and both inflammation and activity scores in infected antral mucosa. A significant positive correlation also was noted between apoptosis and H. pylori density. Serum nitrite concentrations were decreased significantly by successful eradication of H. pylori, and showed a strong positive correlation with H. pylori density. Serum nitrite concentrations showed a significant positive correlation with numbers of single-stranded DNA-positive cells. CONCLUSIONS: High H. pylori density was associated with elevated serum nitrate-plus-nitrite (a marker of nitric oxide production in gastric mucosa). Increased apoptosis and abnormal gastric cell turnover are likely results.

Adult↗

PubMed2001

Brimonidine and inhibition of nitrite production in isolated porcine ciliary processes.

PURPOSE: To investigate whether the alpha 2-adrenoreceptor agonist brimonidine (a drug that decreases intraocular pressure in part by reducing aqueous humor production) can inhibit the production of nitrite induced by forskolin in isolated porcine ciliary processes. METHODS: Nitrite (a metabolite of nitric oxide) was measured (Griess reaction) before and two hours after exposure to the adenylcyclase activator forskolin (0.1 microM) in the presence or in the absence of the brimonidine (10 microM) and/or the alpha 2-adrenoreceptor antagonist yohimbine (10 microM). RESULTS: The increase of nitrite production evoked by forskolin (139 +/- 9%) was significantly (P < 0.01) inhibited by brimonidine (108 +/- 6%). The inhibitory effect of brimonidine on the increase of nitrite production induced by forskolin was significantly (P < 0.01) reversed by yohimbine (136 +/- 7%). CONCLUSIONS: The results of this pilot study suggest that brimonidine inhibits the production of nitrite evoked by forskolin through a mechanism that could involve alpha 2-adrenoreceptor activation in isolated porcine ciliary processes.

Adrenergic alpha-Agonists↗

PubMed2000

Nitric oxide-forming reaction between the iron-N-methyl-D-glucamine dithiocarbamate complex and nitrite.

The objective of this study was to elucidate the origin of the nitric oxide-forming reactions from nitrite in the presence of the iron-N-methyl-D-glucamine dithiocarbamate complex ((MGD)(2)Fe(2+)). The (MGD)(2)Fe(2+) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. Although it is widely believed that only NO can react with (MGD)(2)Fe(2+) complex to form the (MGD)(2)Fe(2+).NO complex, a recent article reported that the (MGD)(2)Fe(2+) complex can react not only with NO, but also with nitrite to produce the characteristic triplet EPR signal of (MGD)(2)Fe(2+).NO (Hiramoto, K., Tomiyama, S., and Kikugawa, K. (1997) Free Radical Res. 27, 505-509). However, no detailed reaction mechanisms were given. Alternatively, nitrite is considered to be a spontaneous NO donor, especially at acidic pH values (Samouilov, A., Kuppusamy, P., and Zweier, J. L. (1998) Arch Biochem. Biophys. 357, 1-7). However, its production of nitric oxide at physiological pH is unclear. In this report, we demonstrate that the (MGD)(2)Fe(2+) complex and nitrite reacted to form NO as follows: 1) (MGD)(2)Fe(2).NO complex was produced at pH 7.4; 2) concomitantly, the (MGD)(3)Fe(3+) complex, which is the oxidized form of (MGD)(2)Fe(2+), was formed; 3) the rate of formation of the (MGD)(2)Fe(2+).NO complex was a function of the concentration of [Fe(2+)](2), [MGD], [H(+)] and [nitrite].

Dose-Response Relationship, Drug↗

PubMed2001

The Structure of an alternative form of Paracoccus pantotrophus cytochrome cd(1) nitrite reductase.

Cytochrome cd(1) nitrite reductase is a bifunctional enzyme, which can catalyze the 1-electron reduction of nitrite to nitric oxide and the 4-electron reduction of dioxygen to water. Here we describe the structure of reduced nitrite reductase, crystallized under anaerobic conditions. The structure reveals substantial domain rearrangements with the c domain rotated by 60 degrees and shifted by approximately 20 A compared with previously known structures from crystals grown under oxidizing conditions. This alternative conformation gives rise to different electron transfer routes between the c and d(1) domains and points to the involvement of elements of very large structural changes in the function in this enzyme. In the present structure, the c heme has a His-69/Met-106 ligation, and this ligation does not change upon oxidation in the crystal. The d(1) heme is penta-coordinated, and the d(1) iron is displaced from the heme plane by 0.5 A toward the proximal ligand, His-200. After oxidation, the iron moves into the d(1) heme plane. A surprising finding is that although reduced nitrite reductase can be readily oxidized by dioxygen in the new crystal, it cannot turnover with its other substrate, nitrite. The results suggest that the rearrangement of the domains affects catalysis and substrate selectivity.

Binding Sites↗

PubMed2006

Intake and food sources of nitrites and N-nitrosodimethylamine in Spain.

OBJECTIVE: To conduct a comprehensive assessment of dietary intakes of nitrites and N-nitrosodimethylamine (NDMA). SUBJECTS AND SETTING: A study was conducted within the Spanish cohort of the European Prospective Investigation in Cancer and Nutrition (EPIC) to assess the intake and food sources of these compounds in Spanish adults. The study included 41,446 health volunteers, aged 29-69 years, from Northern and Southern regions. Usual food intake was estimated by in-person interviews using a computerised dietary questionnaire. RESULTS: The estimated geometric mean was 0.994 mg day(-1) for nitrites and 0.114 microg day(-1) for NDMA. For both compounds a positive trend in consumption with increasing energy intake was observed. Dietary NDMA was related to age and sex after energy adjustment, while nitrite consumption increased with higher intakes of vitamin C (P < 0.001). The food groups that contributed most to intakes were meat products, cereals, vegetables and fruits for nitrites, and processed meat, beer, cheese and broiled fish for NDMA. Current and past smokers, who had high levels of NDMA from tobacco exposure, were also identified as the highest consumers of dietary NDMA. Furthermore, smokers had low intakes of vitamin C (an inhibitor of endogenous nitrosation). CONCLUSIONS: Intake levels of NDMA and nitrites in a Mediterranean cohort are currently relatively lower than those previously reported, although processed meat, beer and cured cheese still are the most important contributors to NDMA intake.

Adult↗

PubMed2006

Nitrite and malondialdehyde content in cerebrospinal fluid of patients with Parkinson's disease.

Evidence from clinical and experimental studies supports the hypothesis of free radical-mediated damage of dopaminergic neurons in the pathology of Parkin's disease (PD). The present study was undertaken to evaluate the role of nitric oxide and oxidative stress in PD. Estimation of the stable metabolites of nitric oxide (NO, nitrite, nitrate) and malondialdehyde (MDA), an acceptable marker of lipid peroxidation, can provide indirect evidence of involvement of free radicals. Nitrite and malondialdehyde (MDA) levels were estimated in the lumbar cerebrospinal fluid (CSF) of 20 controls and 21 patients with PD. Nitrite and MDA content was not significantly altered in the CSF of PD patients as compared to the controls. Nitrite and MDA levels in CSF of PD patients exhibited no correlation with age, duration of disease, and severity of illness (measured by the Unified Parkinson's Disease Rating Score). There was no correlation between the CSF nitrite and MDA level. Findings of the present study do not provide evidence for the involvement of nitric oxide and oxidative stress in PD.

Female↗

PubMed1990

Risk factors of gastric precancerous lesions in a high-risk Colombian population. II. Nitrate and nitrite.

Gastric nitrite content was studied in relation to precancerous lesions of the stomach in a case-control study conducted in a high-risk Colombian population. The proportion of detectable nitrite in gastric juice and the mean pH were significantly higher among those with precancerous lesions (chronic atrophic gastritis, intestinal metaplasia, and dysplasia) than among the controls (normal and superficial gastritis); the proportion and mean pH increased with the progression of histological changes from normal to dysplasia. Nitrite was not detectable in gastric juice with a pH less than 5.0. A positive association was found between the proportion of detectable nitrite and the risk of gastric precancerous lesions. Odds ratios of 4.39 for intestinal metaplasia and 24.72 for dysplasia remained significant after controlling for confounders. This finding suggests that nitrite may be a precursor of a mutagen that targets gastric epithelial cells.

Case-Control Studies↗

PubMedDate not supplied

Nitrates, nitrites and N-nitrosocompounds: a review of the occurrence in food and diet and the toxicological implications.

Data on occurrence of nitrate, nitrite and N-nitrosocompounds in food and drinking water, and on total dietary intakes are reviewed. Metabolic, toxicological and epidemiological studies are surveyed and the implications with respect to safety evaluation are addressed. It is concluded that, on the basis of recent long-term animal studies and of clinical experience in man, the current Acceptable Daily Intake (ADI) allocated to nitrate by the Joint FAO/WHO Expert Committee on Food Additives of 0-5 mg/kg body weight/day (expressed as sodium nitrate) might be increased to 0-25 mg/kg body weight/day. Based on similar criteria, the ADI for nitrite would be 0-0.1 mg/kg body weight/day (expressed as sodium nitrite). In view of the known carcinogenicity of N-nitrosocompounds, exposure to these compounds in food should be minimized by appropriate technological means, such as lowering the nitrite concentration in preserved foods to the minimum required to ensure microbiological safety and use of inhibitors of nitrosation like alpha-tocopherol or ascorbic acid. Further work is needed to define the minimal levels of nitrite in foods needed to inhibit outgrowth of Clostridium botulinum and toxin production.

Animals↗

PubMed1998

Simultaneous determination of nitrite, nitrate and ascorbic acid in canned vegetable juices by reverse-phase ion-interaction HPLC.

A simple ion-interaction C18 reverse-phase high performance liquid chromatographic method was developed for simultaneous determination of nitrite, nitrate and ascorbic acid in canned vegetable juices. The method makes use of 0.010 M octylammonium orthophosphate as the ion interacting reagent and 20% (v/v) aqueous methanol as the mobile phase. The content of nitrite, nitrate (expressed as nitrite ion and nitrate ion, respectively) and ascorbic acid in commercial brands of canned tomato, carrot and mixed vegetable juices were surveyed. The quantitative results indicated that nitrite was very probably added as a preservative in the canned vegetable juices. The total amount of nitrite and nitrate ion per can in two commercial brands of vegetable juices was found to exceed the acceptable daily intake recommended by the 1996 Joint FAO/WHO Expert Committee on Food Additives for an average adult of 60 kg body weight.

Ascorbic Acid↗

PubMed1997

[Fermentation process during the ensiling of green forage low in nitrate. 2. Fermentation process after supplementation of nitrate, nitrite, lactic acid bacteria and formic acid].

The effect of adding nitrate and nitrite (0.05% and 0.01% N in DM) of two inoculants or formic acid on the ensiling of orchardgrass and a grass-legumes-mixture, both low in nitrate, was proved in two experiments during ensiling starting in an early stage of fermentation silages without additives contained butyric acid, with increasing amounts up to 180 day of storage period. Silages with added nitrate or nitrite (0.1% N in DM) contained no butyric acid despite of a delay in the formation of lactic acid Nitrite was more effective as nitrate (both 0.05% N in DM) to suppress butyric acid fermentation. However, both additives, nitrite and nitrate, increased the lactic acid fermentation. Interpreting this facts it was hypothesized that the clostridia was inhibited by nitrate and nitrite. Addition of inoculants improved the formation of lactic acid, and decreased pH-value in comparison to control silages. The formation of butyric acid was limited, but not suppressed. The effect of inoculants differed in the intensity of fermentation and the formation of by-products of lactic acid fermentation. The effect of formic acid was not sure.

Animal Nutritional Physiological Phenomena↗

PubMed2001

Factors affecting nitrite build-up in nitrifying biofilm reactor.

Nitrite build-up in a nitrifying biofilm reactor for direct denitrification from the nitrite stage was investigated. At least three factors were found to influence the nitrite build-up: (i) the relative specific growth rates of Nitrosomonas to Nitrobacter, microNs/microNb in the biofilm; (ii) the relative initial ratio between Nitrosomonas and Nitrobacter on the support surface, (Mao)Ns/(Mao)Nb; (iii) the level of free ammonia, particularly at greater than 0.1 mg N/l that can be inhibitory to Nitrobacter. Results showed that without free ammonia inhibition, the first two factors determined the degree of nitrite build-up. The effect of (Mao)Ns and (Mao)Nb on nitrification kinetics were more significant than the specific growth rates of Nitrosomonas and Nitrobacter. By regulating effects of these three factors, extremely high concentrations of nitrite build-up could occur in a biofilm reactor. This offers a potential for achieving direct denitrification through a nitrate shunt.

Ammonia↗

PubMed2003

Nitrogen removal via nitrite at normal temperature in A/O process.

In order to study the nitrogen removal via nitrite at normal temperature in anoxic/oxic (A/O) process for treating domestic wastewater, the influence of pH, free ammonia (FA), dissolved oxygen (DO), and hydraulic retention time (HRT) were studied. Results indicated that it was possible to remove nitrogen via nitrite in A/O process, if the temperature was between 18 and 25 degrees C and pH was below 7.5. Even if FA was as low as 0.06 mg NH3-N/L, it would inhibit the nitrobacteria. However, FA could not be the sole factor. Whether denitrification went thoroughly or not could affect the nitrification pathway. If denitrification went well, nitrite accumulation could recover in a short while. Nitritification lagged nitratification, so that short HRT would help nitrite accumulation. On the other hand, extended aeration would reduce nitrite accumulation.

Nitrites↗

PubMed1997

Nitrite-induced photo-oxidation of thiol and its implications in smog toxicity to the eye: prevention by ascorbate.

Studies have been conducted on nitrite-induced oxidation of corneal thiols and reduced glutathione (GSH). Oxidation of GSH in the presence of nitrite (NaNO2) was minimal in the dark. Exposure of GSH to UV (365 nm) in the presence of nitrite substantially accelerated this oxidation; only < 10% of the original GSH remained at the end of 20 minutes. A similar Thiol depletion was observed in the case of corneal epithelial extracts irradiated with UV in the presence of the nitrite. Nitrite is therefore considered to be a potent phototoxicant with possible pathophysiological implications to the external eye tissues. Ascorbate was found to be effective in preventing thiol oxidation, suggesting the possibility of preventing nitrogen oxide-based smog irritation to the eye by this physiologically compatible antioxidant.

Animals↗

PubMed1988

Explanation of the discrepancy between the degree of organic nitrate decomposition, nitrite formation and guanylate cyclase stimulation.

We continuously studied the quantitative formation of nitric oxide (NO), nitrite and nitrate ions from several organic nitrate esters in the presence of various thiol-containing compounds by spectroscopy and HPLC. The results indicate that there are different pathways of decomposition depending on the chemical nature of the mercaptan tested. The amino acid cysteine is known to function as an essential cofactor for guanylate cyclase activation by organic nitrates in vitro. For comparison we investigated several structural analogues with respect to their nitric oxide or nitrite ion releasing potency. Both were found to represent the main products resulting from nitrate ester breakdown besides the respective alcohols. We found that only those compounds were able to activate the enzyme in the presence of nitroglycerin (GTN) which induce the release of NO as well. On the other hand, nearly all other thiols tested caused an in vitro decomposition of organic nitrates by producing excess nitrite and the corresponding disulfide without the formation of NO. Thus, the decomposition of organic nitrates to nitrite ions does not contribute at all to activation of guanylate cyclase. Our results confirm that the liberation of nitric oxide is the common principle of action for all nitrovasodilators. In addition, our results suggest that the thiol consuming transformation of organic nitrates into nitrite ions (ratio NO/nitrite 1:10) may lead to a depletion of cysteine stores, resulting in a decreased formation of NO and, consequently, in a decrease of guanylate cyclase activation, clinically arising as nitrate tolerance.

Animals↗

PubMedDate not supplied

Evaluation of reagent strips for the rapid diagnosis of nitrite poisoning.

Two commercial urine test strips based on the Griess nitrite-specific diazonium salt reaction, having sulfanilamide and para-arsanilic acid as substrates, respectively, were studied as qualitative tests in the rapid diagnosis of nitrite/nitrate poisoning. Their usefulness was compared to other rapid tests, such as the sulfanilic acid-1 naphthylamin and diphenylamine blue tests. The practical sensitivity limit to nitrites in plasma and in water of both the reagent strips and SA-1NA test was 0.50 micrograms NO2/mL, while the diphenylamine test, which is not nitrite specific, showed a positive reaction to nitrites in plasma and in water above 50 micrograms NO2/mL and 5 micrograms NO2/mL, respectively. The in vitro assays were evaluated in vivo by the sublethal intoxication of a sheep with nitrite, demonstrating that commercial urine test strips may be useful for the rapid diagnosis of nitrite/nitrate poisoning.

Evaluation Studies as Topic↗

PubMedDate not supplied

The measurement of nitrite in adulterated urine samples by high-performance ion chromatography.

With the increased availability of nitrite-containing commercial products that are used for the adulteration of urine samples in the workplace, it is necessary for laboratories to be able to detect and confirm the presence of nitrite in these samples. We have developed a method to confirm the presence of nitrite in urine samples. The method uses the IonPac AS 14 analytical column with the Dionex series 45001 Bio LC system equipped with an anion self-generating suppressor and conductivity detector. Using a single-point calibration, the method is linear and accurately quantitates nitrite to 12,000 microg/mL. The limit of detection is 30 microg/mL, and the day-to-day precision of the assay has a coefficient of variation (CV) of 4.3% at 1200 microg/mL and 3.8% at 2700 microg/mL of nitrite.

Anions↗