Role of endogenous nitric oxide in airflow obstruction in smokers

Modulation of Lung Function by Increased Nitric Oxide Production

INTRODUCTION

Cigarette smoking reduces endogenous Nitric Oxide (NO) production by reducing Nitric Oxide Synthase (NOS) activity, which is one of the probable reason for increased rate of pulmonary diseases in smokers. Nitric oxide/oxygen blends are used in critical care to promote capillary and pulmonary dilation to treat several pulmonary vascular diseases. Among several supplements, the highest NOS activation has been proved for garlic with its unique mechanism of action.

AIM

To investigate the effect of dietary supplementation of NO producing garlic on pulmonary function of smokers.

MATERIALS AND METHODS

The study was conducted on 40 healthy non-smoker (Group A) and 40 chronic smoker (Group B) males with matched age, height and weight. The pulmonary function tests- Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), FEV1/FVC ratio and Peak Expiratory Flow Rate (PEFR) were performed in non-smokers (Group A), smokers (Group B) and smokers after supplementation of approximately 4 gm of raw garlic (2 garlic cloves) per day for three months (Group C). Endogenous NO production was studied in smokers before and after garlic supplementation and in non-smokers without supplementation. The data obtained were compared between the groups using unpaired student's t-test. The p-value considered significant at <0.05.

RESULTS

Our results showed that FVC, FEV1, FEV1/FVC ratio and PEFR were reduced significantly along with a significant decreased NOS activity among smokers (Group B) when compared with non-smokers (Group A). Garlic supplementation significantly improved the pulmonary function tests in Group C in comparison to Group B by increasing NOS activity.

CONCLUSION

Dietary supplementation of garlic, which might be by increasing NOS activity, has significantly improved pulmonary functions in smokers.

Smoking, COPD, and 3-nitrotyrosine levels of plasma proteins

BACKGROUND

Nitric oxide is a physiological regulator of endothelial function and hemodynamics. Oxidized products of nitric oxide can form nitrotyrosine, which is a marker of nitrative stress. Cigarette smoking decreases exhaled nitric oxide, and the underlying mechanism may be important in the cardiovascular toxicity of smoking. Even so, it is unclear if this effect results from decreased nitric oxide production or increased oxidative degradation of nitric oxide to reactive nitrating species. These two processes would be expected to have opposite effects on nitrotyrosine levels, a marker of nitrative stress.

OBJECTIVE

In this study, we evaluated associations of cigarette smoking and chronic obstructive pulmonary disease (COPD) with nitrotyrosine modifications of specific plasma proteins to gain insight into the processes regulating nitrotyrosine formation.

METHODS

A custom antibody microarray platform was developed to analyze the levels of 3-nitrotyrosine modifications on 24 proteins in plasma. In a cross-sectional study, plasma samples from 458 individuals were analyzed.

RESULTS

Average nitrotyrosine levels in plasma proteins were consistently lower in smokers and former smokers than in never smokers but increased in smokers with COPD compared with smokers who had normal lung-function tests.

CONCLUSIONS

Smoking is associated with a broad decrease in 3-nitrotyrosine levels of plasma proteins, consistent with an inhibitory effect of cigarette smoke on endothelial nitric oxide production. In contrast, we observed higher nitrotyrosine levels in smokers with COPD than in smokers without COPD. This finding is consistent with increased nitration associated with inflammatory processes. This study provides insight into a mechanism through which smoking could induce endothelial dysfunction and increase the risk of cardiovascular disease.

Fractional exhaled nitric oxide in asthma: an update

In asthma, clinical symptoms and lung function are insensitive in reflecting the underlying airway inflammation, and monitoring of this process has only recently become available. Fractional exhaled nitric oxide (Fe(NO)) is now recognized as a reliable surrogate marker of eosinophilic airway inflammation and offers the advantage of being completely non-invasive and very easy to obtain. This review summarizes the clinical use of Fe(NO) in asthma. It covers the relationship between Fe(NO) and the underlying eosinophilic inflammation, the pathophysiology and production of Fe(NO), technical aspects of Fe(NO) measurement and potential confounding factors in interpreting levels. Fe(NO) reference values and the role of Fe(NO) in asthma assessment, diagnosis and management are also discussed.

Role of exhaled nitric oxide in asthma

Nitric oxide (NO), an evanescent atmospheric gas, has recently been discovered to be an important biological mediator in animals and humans. Nitric oxide plays a key role within the lung in the modulation of a wide variety of functions including pulmonary vascular tone, nonadrenergic non-cholinergic (NANC) transmission and modification of the inflammatory response. Asthma is characterized by chronic airway inflammation and increased synthesis of NO and other highly reactive and toxic substances (reactive oxygen species). Pro- inflammatory cytokines such as TNFalpha and IL-1beta are secreted in asthma and result in inflammatory cell recruitment, but also induce calcium- and calmodulin-independent nitric oxide synthases (iNOS) and perpetuate the inflammatory response within the airways. Nitric oxide is released by several pulmonary cells including epithelial cells, eosinophils and macrophages, and NO has been shown to be increased in conditions associated with airway inflammation, such as asthma and viral infections. Nitric oxide can be measured in the expired air of several species, and exhaled NO can now be rapidly and easily measured by the use of chemiluminescence analysers in humans. Exhaled NO is increased in steroid-naive asthmatic subjects and during an asthma exacerbation, although it returns to baseline levels with appropriate anti-inflammatory treatment, and such measurements have been proposed as a simple non-invasive method of measuring airway inflammation in asthma. Here the chemical and biological properties of NO are briefly discussed, followed by a summary of the methodological considerations relevant to the measurement of exhaled NO and its role in lung diseases including asthma. The origin of exhaled NO is considered, and brief mention made of other potential markers of airway inflammation or oxidant stress in exhaled breath.

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.

Increased exhaled nitric oxide in patients with stable chronic obstructive pulmonary disease

BACKGROUND

Nitric oxide (NO) plays an important role as an inflammatory mediator in the airways. Since chronic obstructive pulmonary disease (COPD) is characterised by airway inflammation, a study was undertaken to determine NO levels in the exhaled air of patients with COPD.

METHODS

Two groups of patients with clinically stable COPD were studied, 10 current smokers and 10 ex-smokers. Two control groups of healthy subjects consisting of 10 current smokers and 20 non-smokers were also studied. Exhaled NO levels were measured by the collection bag technique and NO chemiluminescence analyser.

RESULTS

Mean (SE) levels of exhaled NO in ex-smokers and current smokers with COPD (25.7 (3.0) ppb and 10.2 (1.4) ppb, respectively) were significantly higher than in non-smoker and current smoker control subjects (9.4 (0.8) ppb and 4.6 (0.4) ppb, respectively). In current smokers with COPD exhaled levels of NO were significantly lower than in ex-smokers. In this latter group of patients there was a significant negative correlation between smoking history (pack years) and levels of exhaled NO (r = -0.8, p = 0.002). A positive correlation was seen between forced expiratory volume in one second (FEV1) and levels of exhaled NO (r = 0.65, p = 0.001) in patients with COPD.

CONCLUSIONS

These data show that exhaled NO is increased in patients with stable COPD, both current and ex-smokers, compared with healthy control subjects.

Guinea pig airway hyperresponsiveness induced by blockade of the angiotensin II type 1 receptor. Role for endogenous nitric oxide

Losartan is the first angiotensin II type 1 (AT1) receptor antagonist to become available for the treatment of hypertension. However, recent reports have revealed several cases of losartan-induced bronchoconstriction. We investigated to determine the mechanism of losartan-induced bronchoconstriction, considering in particular the involvement of endogenous nitric oxide (NO). In this study, we examined the effects of losartan on airway obstruction and endogenous NO production using anesthetized guinea pigs and cultured airway epithelial cells. Five minutes after administration of angiotensin II (Ang II), the bronchoconstriction induced by acetylcholine was not changed. In contrast, Ang II in the presence of losartan caused a significant increase in the acetylcholine responsiveness. Pretreatment with L-N omega-nitroarginine-methylester (L-NAME) potentiated acetylcholine-induced bronchoconstriction 5 min after administration of Ang II, and L-arginine reversed this action of L-NAME on the acetylcholine responsiveness. Moreover, Ang II administration increased NO concentration in expired air (12.5 +/- 1.5 ppb for saline, 40 +/- 5 ppb for Ang II, p < 0.01), and losartan significantly inhibited Ang II-stimulated NO release (20 +/- 3.5 ppb) from guinea pig airway. In cultured airway epithelial cells, Ang II also increased NO release (160 +/- 25 nM), and the effect of this Ang II-induced NO release was significantly inhibited by pretreatment with losartan (25 +/- 8 nM, p < 0.01). These findings suggest that losartan-induced bronchoconstriction may result from inhibition of endogenous NO release in the airway.

Nitric oxide production and absorption in trachea, bronchi, bronchioles, and respiratory bronchioles of humans

Different volumes of dead-space gas were collected and analyzed for nitric oxide (NO) content, either immediately after inspiration or after a period of breath holding on clean air or NO mixtures. This allowed calculation of NO equilibrium, NO production, and NO absorption. In seven young, healthy, adult nonsmokers, the mean NO equilibrium values in parts per billion (ppb) were 56 +/- 11 (SE) in the trachea, 37 +/- 6 in the bronchi, 21 +/- 3 in the bronchioles, and 16 +/- 2 in the respiratory bronchioles. At any given NO concentration, the NO absorption rate (in nl/min) equaled the NO concentration (in ppb) times A (the absorption coefficient in l/min). A values (in l/min) were 0.11 +/- 0.01 in the trachea, 0.17 +/- 0. 04 in the bronchi, 0.66 +/- 0.09 in the bronchioles, and 1.35 +/- 0. 32 in the respiratory bronchioles. NO equilibrium concentrations and production rates in one 74-yr-old subject were three to five times as high as those found in the young subjects. Mouth equilibrium NO concentrations were 3 and 6 parts per million in two subjects who had oral production rates of 6 and 23 nl/min, respectively. In conclusion, production and absorption of NO occur throughout the first 450 ml of the airways.

Increased production of endogenous nitric oxide in patients with bronchial asthma and chronic obstructive pulmonary disease

BACKGROUND

Nitric oxide (NO) plays an important role as an inflammatory mediator in the airways. Though direct measurement of endogenous NO has been difficult in humans, we have recently found that measurement of NO derivatives in induced sputum may be useful for assessing airway inflammation in asthmatic patients.

OBJECTIVE

This study was designed to determine the direct in vivo evidence of increased production of endogenous NO in patients with bronchial asthma and chronic obstructive pulmonary disease (COPD).

METHODS

We have investigated simultaneous assessment of NO using two non-invasive methods, such as NO level in exhaled air and induced sputum, in these patients. We determined the concentration of stable end-products of NO (nitrite plus nitrate) in induced sputum and exhaled NO concentration using a chemiluminescence analyser in 10 normal controls, 10 asthmatic patients and 11 patients with COPD, and evaluated whether endogenous NO levels correlate with percentage of neutrophils and interleukin-8 (IL-8) level in induced sputum in patients with COPD.

RESULTS

We found significantly higher concentrations of exhaled NO in patients with bronchial asthma (25.1 [5.1] p.p.b.) than in patients with COPD (12.1 [1.9] p.p.b.) and normal controls (5.2 [1.4] p.p.b.). However, higher concentrations of NO derivatives in induced sputum were found in patients with bronchial asthma (1190 [106] micromol/L) and COPD (950 [105] micromol/L) than in normal controls (514 [30] micromol/L). In patients with asthma, but not in those with COPD, concentrations of NO derivatives in induced sputum were significantly correlated with concentrations of exhaled NO (r = 0.64, P < 0.05). Moreover, in patients with COPD, concentrations of NO derivatives in induced sputum were significantly correlated with percentage of neutrophils (r = 0.71, P < 0.05) and IL-8 level (r = 0.80, P < 0.01).

CONCLUSION

We conclude the increased production of endogenous NO in patients with asthma and COPD, and that NO derivatives in induced sputum are more valuable than exhaled NO in assessing airway inflammation in patients with COPD.

Exhaled nitric oxide in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow obstruction and a neutrophilic inflammation. Exhaled nitric oxide (NO) may be a marker of disease activity in a variety of lung diseases. We measured exhaled NO in patients with documented COPD and investigated whether the concentration of exhaled NO is related to the severity of disease as defined by lung function. We also investigated whether concentration of exhaled NO was different in COPD patients who received inhaled steroids compared with steroid-naive patients. We studied 13 current smokers with COPD, eight exsmokers with COPD, 12 patients with unstable COPD (exacerbation or severe disease), and 10 smokers with chronic bronchitis without airflow limitation. Exhaled NO levels were significantly higher in patients with unstable COPD (12.7 +/- 1.5 ppb) than in other groups (p < 0.01). Exhaled NO levels were significantly higher in smokers with COPD than in smokers with chronic bronchitis (4.3 +/- 0.5 versus 2.5 +/- 0.5 ppb, p < 0.05), and were even higher in patients with COPD who had stopped smoking (6.3 +/- 0.6 ppb, p < 0.01). Exhaled NO levels showed a significant negative correlation with their lung function assessed by % predicted FEV1 values (r = -0.6, p < 0.001). Exhaled NO levels in patients treated with inhaled steroids were significantly higher compared with steroid-naive patients (8.2 +/- 1.2 ppb versus 5 +/- 0.4 ppb, p < 0.05), but the first group included more severe patients as assessed by lung function. We conclude that exhaled NO could serve as a useful, practical marker for monitoring disease activity in COPD.

Exhaled pentane and nitric oxide levels in patients with obstructive sleep apnea

BACKGROUND

Upper airway inflammation is present in patients with obstructive sleep apnea (OSA).

OBJECTIVE

To determine whether exhaled pentane and nitric oxide (NO) levels, two nonspecific markers of inflammation, are increased in patients with OSA.

METHODS

Exhaled nasal and oral pentane and NO levels were determined before and after sleep in 20 patients with OSA (apnea-hypopnea index, 48+/-7; mean+/-SEM) and eight healthy control subjects.

RESULTS

In patients with OSA, exhaled nasal and oral pentane levels after sleep were significantly higher than presleep values (6.1+/-1.2 nM vs 3.4+/-0.4 nM, and 7.0+/-1.3 nM vs 4.2+/-0.4 nM, respectively; p<0.05). Likewise, exhaled nasal and oral NO levels after sleep were significantly higher than presleep values in patients with OSA (39.7+/-3.8 ppb vs 28.4+/-2.9 ppb and 10.9+/-1.5 ppb vs 6.6+/-0.8 ppb, respectively; p<0.05). By contrast, there were no significant differences in exhaled nasal and oral pentane, and nasal NO levels before and after sleep in control subjects. Exhaled oral NO levels were significantly increased after sleep in comparison to presleep values in control subjects (p<0.05).

CONCLUSION

Exhaled nasal pentane and NO levels are increased after sleep in patients with moderate-severe OSA. These data suggest that upper airway inflammation is present in these patients after sleep.