Metabolites of nitric oxide in the lower respiratory tract of children

Dynamic thiol/disulfide homeostasis in children with community-acquired pneumonia

BACKGROUND

Alteration in thiol level under oxidative stress may contribute to community-acquired pneumonia (CAP). The goal of this study was to determine whether there are changes in thiol/disulfide homeostasis and nitric oxide (NO) in children with CAP.

METHODS

In total, 130 participants were involved in the study. Of these, 65 had been diagnosed with CAP on admission, and the remaining 65 were healthy individuals. Serum total thiol and native thiol were measured in each participant using a novel automated spectrophotometric method. The amount of dynamic disulfide bonds and related ratios were calculated from these values. Serum NO was measured on chemiluminescence assay.

RESULTS

Average native thiol, total thiol, and disulfide in the CAP group were significantly lower than in the healthy individuals (P < 0.0001, P < 0.0001, P = 0.0126, respectively). In addition, disulfide/native thiol (P = 0.0002), and disulfide/total thiol ratios (P = 0.0004) were significantly higher, whereas the native thiol/total thiol ratio (P = 0.0004) was lower in the CAP group. High serum NO was noted in the CAP group (P = 0.0003), but there was no marked correlation between thiol/disulfide and NO.

CONCLUSION

The changes in endogenous thiol levels under oxidative stress may be associated with the pathogenesis of CAP in pediatric patients.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

A Biomarker-Based Approach to Infectious Disease in the Pediatric Emergency Department

In modern pediatric emergency medicine, biomarker-based assays that enable quick bedside diagnostics and subsequent disease management can be valuable. There is a growing need for novel, disease-specific biomarkers that can improve the outcome of pediatric infectious diseases commonly encountered in the emergency department (ED). Viral respiratory infections, central nervous system infections, sepsis, and septic shock are acute disease states frequently encountered in the ED. In this review, we describe a host of novel biomarkers, including a diverse set of cytokines, chemokines, and nitric oxide–based metabolites. Based on disease pathophysiology, a rationale is provided for a molecular- or biomarker-based approach in the ED. Throughout this review, emphasis is placed on diagnostic rapidity because this relates directly to timeliness and quality of care in a busy ED. Once the biomarkers become more clinically available, in a rapid ED setting as bedside point-of-care assays, quality of care will be enhanced, not only by means of diagnostics but also in prognosticating severity of illness.

Nitric oxide and its metabolites in the critical phase of illness: rapid biomarkers in the making

The potential of nitric oxide (NO) as a rapid assay biomarker, one that could provide a quantum leap in acute care, remains largely untapped. NO plays a crucial role as bronchodilator, vasodilator and inflammatory mediator. The main objective of this review is to demonstrate how NO is a molecule of heavy interest in various acute disease states along the emergency department and critical care spectrum: respiratory infections, central nervous system infections, asthma, acute kidney injury, sepsis, septic shock, and myocardial ischemia, to name just a few. We discuss how NO and its oxidative metabolites, nitrite and nitrate, are readily detectable in several body compartments and fluids, and as such they are associated with many of the pathophysiological processes mentioned above. With methods such as high performance liquid chromatography and chemiluminescence these entities are relatively easy and inexpensive to analyze. Emphasis is placed on diagnostic rapidity, as this relates directly to quality of care in acute care situations. Further, a rationale is provided for more bench, translational and clinical research in the field of NO biomarkers for such settings. Developing standard protocols for the aforementioned disease states, centered on concentrations of NO and its metabolites, can prove to revolutionize diagnostics and prognostication along a spectrum of clinical care. We present a strong case for developing these biomarkers more as point-of-care assays with potential of color gradient test strips for rapid screening of disease entities in acute care and beyond. This will be relevant to global health.

Nitric oxide metabolites as biomarkers for influenza-like acute respiratory infections presenting to the emergency room

AIMS

Nitric oxide (NO) is increased in the respiratory tract in pulmonary infections. The aim was to determine whether nasal wash NO metabolites could serve as biomarkers of viral pathogen and disease severity in children with influenza-like illness (ILI) presenting to the emergency department (ED) during the 2009 influenza A H1N1 pandemic.

METHODS

Children ≤18 years old presenting to the ED with ILI were eligible. Nasal wash specimens were tested for NO metabolites, nitrate and nitrite, by HPLC and for respiratory viruses by real-time PCR.

RESULTS

Eighty-nine patients with ILI were prospectively enrolled during Oct-Dec, 2009. In the entire cohort, nasal wash nitrite was low to undetectable (interquartile range [IQR], 0 - 2 μM), while median nitrate was 3.4 μM (IQR 0-8.6). Rhinovirus (23%), respiratory syncytial virus (RSV) (20%), novel H1N1 (19%), and adenovirus (11%) were the most common viruses found. Children with RSV subtype B-associated ILI had higher nitrate compared to all other viruses combined (P=0.002).

CONCLUSION

Concentration of NO-derived nitrate in nasal secretions in children in the ED is suggestive of viral pathogen causative for ILI, and thus might be of clinical utility. Predictive potential of this putative biomarker for ILI needs further evaluation in sicker patients in a prospective manner.

Induced sputum nitrites correlate with FEV1 in children with cystic fibrosis

AIM

To determine the difference in the levels of nitrites in induced sputum of children with cystic fibrosis (CF) and controls. Furthermore, to evaluate the association between induced sputum nitrites and lung function in children with CF.

METHODS

Nitrites, cell differentials, white blood cell count, were estimated in induced sputum of 20 children with CF and 10 age-matched healthy controls. Nitrites in induced sputum samples were measured using the Greiss assay. Lung function was ascertained by spirometry.

RESULTS

We observed high levels of nitrites in CF (184.8 +/- 11.07 microM/L) versus controls (56.4 +/- 5.7 microM/L) (p < 0.01). A positive correlation between neturophil percent and nitrites, white blood cell count and nitrites (p < 0.05) in children with CF was observed. Sputum nitrites correlated negatively with FEV(1) (p < 0.05) in children with CF.

CONCLUSION

Induced sputum nitrite could serve as a useful non invasive marker for assessing the degree of inflammation in the airways of children with CF.

[Role of oxidative stress in respiratory diseases and its monitoring]

Together with inflammation and subsequent remodeling of airways, an imbalance between oxidative and anti-oxidative agents is generated during the development of numerous pulmonary diseases. This process seems to be involved in both the pathogenesis and chronification of asthma, chronic obstructive pulmonary disease (COPD), SOAS, interstitial lung diseases and cystic fibrosis. Reactive oxygen species including superoxide anion, hidroxyl radicals and hydrogen peroxide (H2O2) are synthetised as a response of inflammatory cells and are responsible of the oxidation of nucleic acids, proteins and membrane lipids, leading to cell damage and enhanced inflammation. Until recently, it was difficult to quantify the airway production of reactive oxidative species (ROS). In fact, it has been only in the last few years when it has been possible to determine indirectly the levels of ROS in expired air and in tissue of asthmatic patients. The analysis of exhaled air is a single, reproducible and non-invasive technique which is useful in the study of volatile and non-volatile gases generated in different conditions. The determination of exhaled nitric oxide and carbon monoxide (CO) has a great usefulness in the assessment of asthma. Nitric oxide seems to be closely related to the physiopathology of asthma and COPD. In fact, it is correlated with the levels of sputum eosinophils and with the response to the treatment with steroids. Yet a correlation with the degree of airflow obstruction and the seriousness of the process has not been found. Exhaled CO is another indirect marker of inflammation and it is increased in asthma, COPD, cystic fibrosis and bronchectases. Even though numerous studies have shown its usefulness as a marker of inflammation and in the response to corticosteroids, its clinical application has limitations. In particular, it is not a specific and exclusive marker of oxidative stress and its levels are highly influenced by tobacco smoke. On the other hand, the association between exhaled CO and FEV1 is not clear and no relationship has been proved so far with the improvement of pulmonary function after steroid therapy and with the decrease of maximum expiratory flow at relapses. In this Review, we describe the advances in the knowledge of oxidative stress as a decisive factor in the pathogenesis of prevalent pulmonary diseases, as well as the methods allowing its analysis and monitoring.

Anaerobic killing of mucoid Pseudomonas aeruginosa by acidified nitrite derivatives under cystic fibrosis airway conditions

Mucoid, mucA mutant Pseudomonas aeruginosa cause chronic lung infections in cystic fibrosis (CF) patients and are refractory to phagocytosis and antibiotics. Here we show that mucoid bacteria perish during anaerobic exposure to 15 mM nitrite (NO2) at pH 6.5, which mimics CF airway mucus. Killing required a pH lower than 7, implicating formation of nitrous acid (HNO2) and NO, that adds NO equivalents to cellular molecules. Eighty-seven percent of CF isolates possessed mucA mutations and were killed by HNO2 (3-log reduction in 4 days). Furthermore, antibiotic-resistant strains determined were also equally sensitive to HNO2. More importantly, HNO2 killed mucoid bacteria (a) in anaerobic biofilms; (b) in vitro in ultrasupernatants of airway secretions derived from explanted CF patient lungs; and (c) in mouse lungs in vivo in a pH-dependent fashion, with no organisms remaining after daily exposure to HNO2 for 16 days. HNO2 at these levels of acidity and NO2 also had no adverse effects on cultured human airway epithelia in vitro. In summary, selective killing by HNO2 may provide novel insights into the important clinical goal of eradicating mucoid P. aeruginosa from the CF airways.

Validation of nitrite and nitrate measurements in exhaled breath condensate

BACKGROUND

Inflammatory markers in exhaled breath condensate (EBC) are investigated as a non-invasive approach to monitoring of inflammation in the respiratory tract. EBC concentrations of nitrite and nitrate, the stable end products of oxidative metabolism of nitric oxide, are increased in patients with asthma, especially during acute exacerbations.

OBJECTIVES

To examine methodological aspects of nitrite and nitrate measurements in EBC such as sample collection, storage and analysis.

METHODS

In a randomized study, EBC was collected twice within 1 h (with and without a nose clip) in 20 healthy adults and 20 patients with well-controlled asthma and no symptoms of allergic rhinitis. Nitrite and nitrate were assayed by ionex chromatography and fluorimetrically after derivatization with diaminonaphthalene.

RESULTS

The geometric mean [exp (mean +/- SD)] EBC levels of nitrite and nitrate in healthy subjects [4.3 (3.0-6.1) and 11.0 (5.3-22.7) micromol/l] and patients [4.6 (2.6-7.3) and 8.7 (3.2-23.8) micromol/l] did not differ (p = 0.13). Wearing a nose clip (p = 0.3) did not influence nitrite and nitrate concentrations. The mean intra-subject %CVs of EBC concentrations of nitrite were 26 and 21% in healthy subjects and patients, while those of nitrate achieved 49 and 88%, respectively.

CONCLUSIONS

Ionex chromatography of nitrite and nitrate requires no sample pretreatment and provides comparable results as a more laborious diaminonaphthalene method. EBC samples should be kept cold (8 degrees C) and analyzed for nitrite and nitrate within 24 h of collection or stored in the freezer and thawed preferably only once. Wearing a nose clip during EBC collection has no influence on nitrite and nitrate concentrations. Short-term repeatability of nitrite and nitrate measurements was worse compared to published data on exhaled nitric oxide.

BALF nitrite as an indicator of inflammation in children with cystic fibrosis

BACKGROUND

A unique substance reflecting the degree of inflammation localized to the lower respiratory tract in patients with cystic fibrosis (CF) has been the concern of several investigators and nitric oxide has gained interest for this purpose in the last decades.

OBJECTIVES

The aim of this study was to evaluate the cytokine and nitrite levels by showing the relationship between them in serum and bronchoalveolar lavage fluid (BALF) of patients with CF and patients in which flexible fiberoptic bronchoscopy (FFB) was applied because of indications other than infection.

METHODS

20 children with CF with mean age 8.2 years and 10 children as control group with mean age 4.2 years were included in the study. Cultures for aerobes, anaerobes, fungi and mycobacteria, cell differentials, cytokine and nitrite measurements were made from BALF specimens. White blood cell (WBC) count, erythrocyte sedimentation rate (ESR), quantitative C-reactive protein (QCRP), cytokine and nitrite levels were measured from serum samples.

RESULTS

BALF neutrophil, TNF-alpha, IL-8 and nitrite levels were significantly higher in patients with CF than control patients. There was no correlation between serum and BALF cytokine and nitrite levels. However, there was a significantly positive correlation between BALF IL-8 and nitrite levels in patients with CF (r = 0.5) and also in control patients (r = 0.6).

CONCLUSIONS

The results suggest that BALF nitrite levels reflect the degree of inflammation localized to lower respiratory tract and may be a useful indicator of airway inflammation for patients with CF.

Nitrate in exhaled breath condensate of patients with different airway diseases

There is an increasing interest in the measurement of nitric oxide (NO.) in the airways. NO. is a free radical that reacts rapidly with reactive oxygen species in aqueous solution to form peroxynitrite which can then break down to nitrite (NO(2)(-)) and nitrate (NO(3)(-)). NO(3)(-) is considered a stable oxidative end product of NO. metabolism. The aim of this study was to assay NO(3)(-) in exhaled breath condensate (EBC) of normal nonsmoking and smoking subjects, asthmatics, patients with obstructive pulmonary disease (COPD), and patients with community-acquired pneumonia (CAP). EBC was collected using a glass condenser and samples were assayed for NO(3)(-) by ion chromatography followed by conductivity measurement. NO(3)(-) was detectable in EBC of all subjects. NO(3)(-) was elevated in smokers [median (range)] [62.5 (9.6-158.0) microM] and in asthmatics [68.0 (25.8-194.6) microM] compared to controls [9.6 (2.6-119.4) microM; p=0.003 and p=0.006, respectively], whereas NO(3)(-) was not elevated in COPD patients [24.1 (1.9-337.0 microM]. The concentration of NO(3)(-) in patients with CAP [243.4 (26.1-584.5) microM] was higher than that in controls (p=0.002) and NO(3)(-) values decreased after treatment and recovery from illness [40.0 (4.1-167.0) microM, p=0.009]. This study shows that NO(3)(-) is detectable in EBC of healthy subjects and it varies in patients with inflammatory airway diseases.

Nitric oxide metabolites in the urine of full-term and preterm infants

BACKGROUND

In newborn full-term and preterm infants the urine nitrites and nitrates (NOx) were measured, in order to investigate the effects of different pathological conditions (infection, hypoxia) on systemic nitric oxide production.

METHODS

Urine nitrites and nitrates were determined by means of the Griess reaction, after reduction of nitrates to nitrites with nitrate reductase.

RESULTS

The NOx level was higher in preterm (278 nmol/mL) than full-term (176 nmol/mL) infants. Low NOx (115 nmol/mL) levels accompanied generalized infections, while its high contents (650 nmol/mL) was found in cytomegalovirus and one case of Pneumocystis carinii infection. Moderate increase of NOx production was observed in infants with local pulmonary infections and encephalopathies.

CONCLUSIONS

The results indicate urinary NOx level is lowered in infants with life-threatening generalized infection. A possibility of a rapid test based on newborn urinary NOx level determination is considered.

Biomarkers of some pulmonary diseases in exhaled breath

Analysis of various biomarkers in exhaled breath allows completely non-invasive monitoring of inflammation and oxidative stress in the respiratory tract in inflammatory lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF), bronchiectasis and interstitial lung diseases. The technique is simple to perform, may be repeated frequently, and can be applied to children, including neonates, and patients with severe disease in whom more invasive procedures are not possible. Several volatile chemicals can be measured in the breath (nitric oxide, carbon monoxide, ammonia), and many non-volatile molecules (mediators, oxidation and nitration products, proteins) may be measured in exhaled breath condensate. Exhaled breath analysis may be used to quantify inflammation and oxidative stress in the respiratory tract, in differential diagnosis of airway disease and in the monitoring of therapy. Most progress has been made with exhaled nitric oxide (NO), which is increased in atopic asthma, is correlated with other inflammatory indices and is reduced by treatment with corticosteroids and antileukotrienes, but not (beta 2-agonists. In contrast, exhaled NO is normal in COPD, reduced in CF and diagnostically low in primary ciliary dyskinesia. Exhaled carbon monoxide (CO) is increased in asthma, COPD and CF. Increased concentrations of 8-isoprostane, hydrogen peroxide, nitrite and 3-nitrotyrosine are found in exhaled breath condensate in inflammatory lung diseases. Furthermore, increased levels of lipid mediators are found in these diseases, with a differential pattern depending on the nature of the disease process. In the future it is likely that smaller and more sensitive analyzers will extend the discriminatory value of exhaled breath analysis and that these techniques may be available to diagnose and monitor respiratory diseases in the general practice and home setting.

Noninvasive monitoring in the pediatric intensive care unit

The best ICU monitors are physicians and nurses, who integrate all of the physiologic parameters of patients with the known pathophysiology of the disease process. Over-reliance on raw electronic data, with their inherent errors, jeopardizes the safe and efficient care of patients. Data must be interpreted in the context of the history, repetitive physical examinations, response to therapy, and a background of experience. New modalities and the application of artificial intelligence may facilitate the interpretation of data, but the role of the bedside medical practitioner remains as the heart of pediatric critical care.

Óxido nítrico exalado no diagnóstico e acompanhamento das doenças respiratórias

O presente trabalho apresenta uma sucinta revisão sobre o papel do óxido nítrico na fisiologia respiratória e na fisiopatologia de algumas pneumopatias. A perspectiva de seu uso para diagnóstico e acompanhamento de inúmeras situações clínicas é discutida.

Exhaled nitric oxide before and after montelukast sodium therapy in school-age children with chronic asthma: a preliminary study

Exhaled nitric oxide (ENO) is a surrogate marker of airway inflammation in asthma. In 12 children aged 6-11 years with mild to moderate persistent asthma, ENO concentrations were measured before and after 4 weeks of treatment with montelukast sodium, a leukotriene receptor antagonist, and 2 weeks after withdrawal of therapy. Baseline ENO levels (mean and 95% confidence interval) were significantly elevated in patients with asthma compared to age-matched nonasthmatic control subjects, with levels of 83 (42-123) vs. 13 (11-15) ppb (P < 0.001). After treatment with montelukast sodium, there was a significant (P < 0.01) reduction in ENO to 58 (27-89) ppb which again rose to 69 (38-99) ppb 2 weeks after treatment was withdrawn. During treatment, the fall in ENO was accompanied by nonsignificant improvements in prebronchodilator forced expiratory volume in 1 s (FEV(1)) from 81-85% predicted or reductions in use of albuterol from a mean of 2.5 to 1.6 puffs/day. Individual ENO measurements and change in ENO concentrations with treatment did not correlate with either pulmonary function changes or use of bronchodilator. These data show that ENO is elevated in children with relatively mild asthma treated with bronchodilator alone, and that treatment with montelukast sodium for 4 weeks results in a significant reduction in ENO concentrations, even in the absence of significant changes in pulmonary function. These findings suggest an anti-inflammatory role for leukotriene D(4) receptor antagonism in the treatment of children with mild to moderate asthma.

Cystic fibrosis lung disease: the role of nitric oxide

This review summarizes current knowledge about the role of nitric oxide (NO) in cystic fibrosis (CF) lung disease. NO is endogenously produced by a group of enzymes, the NO synthases (NOSs). There are three isoforms of NOS, each encoded by different genes: neuronal (nNOS), immune or inducible (iNOS), and endothelial (eNOS) nitric oxide synthase.(1) They all form NO and L-citrulline by enzymatic oxidation of L-arginine. This reaction requires a number of cosubstrates, including molecular oxygen and tetrahydrobiopterin. It is now known whether all three isoenzymes are constitutively expressed in cells of the respiratory tract and that their gene expression is inducible.(2,3) NO production by iNOS, the "high-output" NOS, is stimulated by bacterial lipopolysaccharide (LPS) as well as proinflammatory cytokines such as interleukin (IL)-1gamma, IL-2, interferon (IFN)-gamma, and tumor necrosis factor (TNF). In contrast to nNOS and eNOS, activation of iNOS does not require an increase in intracellular Ca(2+) concentration.

Concentration of nitric oxide products in bronchoalveolar fluid obtained from infants who develop chronic lung disease of prematurity

AIMS

To determine if nitric oxide (NO) products (nitrate and nitrite) are increased in bronchoalveolar lavage (BAL) fluid obtained from infants who develop chronic lung disease of prematurity (CLD).

METHODS

One hundred and thirty six serial bronchoalveolar lavages were performed on 37 ventilated infants (12 with CLD, 18 with respiratory distress syndrome (RDS), and seven control infants) who did not receive inhaled NO.

RESULTS

During the first week of life nitrate concentration was between 25-31 micromol/l in all three groups. Thereafter, the concentration of BAL fluid nitrate decreased to 14 micromol/l and 5.5 micromol/l, respectively in the RDS and control groups by 14 days of age. In contrast, nitrate in the CLD infants remained constant until 28 days of age (31.3 micromol/l at day 14; p<0.05). In all BAL fluid samples the mean concentration of nitrite was <1.2 micromol/l throughout the first 28 days with no significant differences noted among the three groups.

CONCLUSION

The similar concentration of BAL fluid nitrate in all groups during the first week of life suggest that NO may be important in the adaptation of the pulmonary circulation after birth. However, persistence of nitrate in the BAL fluid of infants with CLD during the second week may reflect pulmonary maladaptation, or, more likely, persisting pulmonary inflammation.

Nitrite levels in breath condensate of patients with cystic fibrosis is elevated in contrast to exhaled nitric oxide

BACKGROUND

Nitric oxide (NO) is released by activated macrophages, neutrophils, and stimulated bronchial epithelial cells. Exhaled NO has been shown to be increased in patients with asthma and has been put forward as a marker of airways inflammation. However, we have found that exhaled NO is not raised in patients with cystic fibrosis, even during infective pulmonary exacerbation. One reason for this may be that excess airway secretions may prevent diffusion of gaseous NO into the airway lumen. We hypothesised that exhaled NO may not reflect total NO production in chronically suppurative airways and investigated nitrite as another marker of NO production.

METHODS

Breath condensate nitrite concentration and exhaled NO levels were measured in 21 clinically stable patients with cystic fibrosis of mean age 26 years and mean FEV1 57% and 12 healthy normal volunteers of mean age 31 years. Breath condensate was collected with a validated method which excluded saliva and nasal air contamination and nitrite levels were measured using the Griess reaction. Exhaled NO was measured using a sensitive chemiluminescence analyser (LR2000) at an exhalation rate of 250 ml/s. Fourteen patients with cystic fibrosis had circulating plasma leucocyte levels and differential analysis performed on the day of breath collection.

RESULTS

Nitrite levels were significantly higher in patients with cystic fibrosis than in normal subjects (median 1.93 microM compared with 0.33 microM). This correlated positively with circulating plasma leucocytes and neutrophils (r = 0.6). In contrast, exhaled NO values were not significantly different from the normal range (median 3.8 ppb vs 4.4 ppb). There was no correlation between breath condensate nitrite and lung function and between breath condensate nitrite and exhaled NO.

CONCLUSIONS

Nitrite levels in breath condensate were raised in stable patients with cystic fibrosis in contrast to exhaled NO. This suggests that nitrite levels may be a more useful measure of NO production and possibly airways inflammation in suppurative airways and that exhaled NO may not reflect total NO production.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Nitric oxide metabolites in cystic fibrosis lung disease

Although the activity of nitric oxide (NO) synthases are increased in lung tissue of patients with cystic fibrosis, the concentrations of nasal and exhaled NO have recently been found to be decreased in cystic fibrosis. This could either be due to reduced NO formation or metabolism of NO within airway fluids. In this study, the stable NO metabolites, nitrate and nitrite, were determined in the saliva and sputum of 18 stable cystic fibrosis patients, 21 cystic fibrosis patients during a pulmonary exacerbation, and in saliva and endotracheal secretions of normal controls. Median saliva concentrations of NO metabolites (nitrate plus nitrite) were 704 mumol/l (95% confidence interval (CI) 419 to 1477) in stable cystic fibrosis patients, 629 mumol/l (95% CI 382 to 1392) in cystic fibrosis patients presenting with pulmonary exacerbation, and 313 mumol/l (95% CI 312 to 454) in controls. Median sputum NO metabolite concentration in stable cystic fibrosis was 346 mumol/l (95% CI 311 to 504). This was not significantly different from cystic fibrosis patients presenting with pulmonary exacerbation (median 184 mumol/l, 95% CI 249 to 572), but significantly higher than in endotracheal secretions of controls (median 144 mumol/l, 95% CI 96 to 260). Sputum NO metabolite concentration in cystic fibrosis pulmonary exacerbation significantly increased during antibiotic treatment. A positive correlation was observed between sputum NO metabolites and lung function in stable cystic fibrosis, suggesting less airway NO formation in cystic fibrosis patients with more severe lung disease. These data indicate that decreased exhaled NO concentrations in cystic fibrosis patients may be due to retention and metabolism of NO within the airway secretions. However, sputum NO metabolites are not a useful marker of airway inflammation in cystic fibrosis lung disease.