Comparison of fetal plasma cortisol level between eutrophic and hypotrophic newborns

We tested two groups of singletons born at term: fifty-six eutrophic newborns and 56 hypotrophic subjects. They were selected randomly from all newborns delivered by vaginal route between 8 and 14 hours. Excluded were preeclampsia, diabetes, labours longer than 12 hours and newborns with malformations. Written informed consent was obtained from all women and data were collected before and after labour. Umbilical cord blood samples were obtained immediately following the delivery and plasma cortisol concentrations were measured by radioimmunoassay. The groups did not differ significantly regarding maternal age, parity, gestational age and Apgar score, but birth weight was significant differed (p < 0.001). In addition, eutrophic newborns had significantly elevated cortisol levels (457.7 nmol/L, 321.8-696.6 nmol/L) compared with hypotrophic newborns (320.5 nmol/L, 215.1-578.7 nmol/L, p < 0.001). The role of fetal cortisol in intrauterine growth restriction (IUGR) pregnancy and labour is uncertain, but fetal plasma cortisol levels may be lower in IUGR newborns.     

Nitric oxide production in newborns under phototherapy.

Nitrogen monoxide (NO) is a potent endogenous vasodilator and is involved in cytotoxicity, neurotransmission, and immunological defense mechanisms. Phototherapy has long been known to change the distribution of blood flow throughout the body in newborn infants. The objective of this study was to investigate the effect of phototherapy on NO production in otherwise healthy newborns. Urinary NO levels were measured before and 6 h after phototherapy by a chemiluminescence method using Sievers NOA. Ten newborns (gestational age, 36.4 +/- 3.9 weeks; birth weight, 2863 +/- 677.44 g; postnatal age, 5.1 +/- 2.72 days) were started on phototherapy according to AAP guidelines and urine for NO measurement was collected prior to therapy and 6 h after the commencement of treatment. Urinary NO levels measured during phototherapy were significantly higher (108.8+/-50.69 micromol/mmol creatinine) than the levels measured before phototherapy (73.13+/-34.15 micromol/mmol creatinine; P < 0.05). These results suggest that newborns receiving phototherapy might have increased NO production, which might result in hemodynamic changes. However, further studies on the effects of phototherapy on NO and photorelaxation are needed before reaching firm conclusions.     

A simple method to sample exhaled NO not contaminated by ambient NO from children and adults in epidemiological studies.

We previously showed that contamination of exhaled air by ambient NO could be avoided by 1 min of breathing and final inhalation of clean air (clean air procedure) prior to exhaled air sampling in balloons. This approach is, however, unsuitable for sampling large groups in epidemiological studies, because it is time consuming and laborious. We therefore discarded the initial part of exhaled air, which may contain ambient NO, in prebags of 250, 540, 775, 1000, and 2000 ml. The subsequent part of exhaled air was sampled in balloons and the NO content was measured. Inflation of a prebag of 500 ml to prevent ambient NO contamination proved to be effective only at low ambient NO levels (<20 ppb). Larger sizes of the prebag (1000 ml for adults and 775 ml for children) are, however, required so that contamination of the air sample at higher levels of ambient NO (up to 115 ppb) is excluded. Using different prebags of gradually increasing size, it was shown that the initial part of exhaled air (<500 ml) contained relatively high amounts of NO that gradually decreased, but attained a constant level in the subsequent air volumes. Using rather large prebags of 2000 and 1000 ml, respectively, in adults and children yielded exhaled NO levels even below those obtained the clean air procedure was applied in combination with a prebag of 540 ml. As this reduction also occurs at ambient NO levels of nearly zero, we suggest that this reduction was due to interference by the water vapor arising from the lowest part of the lungs. In conclusion, the use of a prebag to discard the initial volume of exhaled air ensures accurate measurement of exhaled endogenous NO in large-scale epidemiological studies not biased by ambient NO.     

Endotoxaemia in rats: role of NO, PAF and TXA2 in pulmonary neutrophil sequestration and hyperlactataemia.

OBJECTIVE AND DESIGN: The involvement of PAF, TXA2 and NO in LPS-induced pulmonary neutrophil sequestration an hyperlactataemia was studied in conscious rats. As pharmacological tools WEB 2170 (PAF receptor antagonist, 20 mg/kg), camongarel (inhibitor of TXA2 synthase, 30 mg/kg), N(G)-nitro L-arginine methyl ester (L-NAME -- non-selective nitric oxide synthase inhibitor, 30 mg/kg) were used. METHODS: Plasma lactate and NO2-/NO3- levels as well as myeloperoxidase (MPO) activity in lung tissue were measured one and five hours after administration of LPS (4 mg/kg(-1)). RESULTS: LPS induced a twofold increase in plasma lactate levels and nearly 10-fold increase in plasma NO2-/NO3- levels five but not one hour after LPS administration. However, LPS-induced increase in pulmonary MPO activity was seen at both time intervals. Neither WEB 2170 nor camonagrel changed one or five hours responses to LPS (lactate, NO2-/NO3-, MPO). L-NAME potentiated LPS-induced rise in MPO activity in the lung and this potentiation was not affected by WEB 2170 or camonagrel. L-NAME supressed plasma NO2-/NO3- response and substantially potentiated plasma lactate response to LPS and both effects were partially reversed by WEB 2170 or camonagrel. CONCLUSIONS: In summary, we demonstrated that PAF and TXA 2 play a role in overproduction of lactate during endotoxaemia in NO-deficient rats. However, these lipids do not mediate endotoxin-induced sequestration of neutrophils in the lung.     

Plasma F2-isoprostanes are elevated in newborns and inversely correlated to gestational age

F(2)-isoprostanes, prostaglandin F(2)-like compounds formed by free radical-catalyzed lipid peroxidation, are considered the most reliable markers of oxidative stress. It has been repeatedly suggested that newborns are exposed to conditions of oxidative stress resulting from the change from a low oxygen pressure in utero to a high oxygen pressure at birth. We measured the levels of F(2)-isoprostanes in plasma of newborns by gas chromatography/mass spectrometry and we found that F(2)-isoprostanes are significantly higher in term newborns compared to healthy adults. The greatest values were found in preterm newborns in whom F(2)-isoprostanes are even higher than in term babies. Moreover a significant inverse correlation was found between the plasma levels of isoprostanes and the gestational age. A quite normal level of isoprostanes was found in the mothers both at delivery and during pregnancy. Placental total F(2)-isoprostanes (sum of free plus esterified) were significantly higher in preterm compared to term deliveries and such a difference might account for the difference in plasma isoprostanes. Plasma non-protein-bound iron is higher in preterm than in term newborns, even if no correlation was found with plasma F(2)-isoprostanes. Erythrocyte desferrioxamine-chelatable iron content (0 time) and release (24 h of aerobic incubation) are higher in newborns than in adults and in preterm than in term newborns, but again no correlation was found with plasma F(2)-isoprostanes. The marked increase in plasma isoprostanes suggests that oxidative stress is a feature of the physiopathological changes seen in the perinatal period.     

Decreased exhaled nitric oxide as a marker of postinsult immune paralysis.

Nitric oxide (NO) regulates neutrophil migration and alveolar macrophage functions such as cytokine synthesis and bacterial killing, both of which are impaired in immune paralysis associated with critical illness. The aim of this study was to determine whether NO is involved in immune paralysis and whether exhaled NO measurement could help to monitor pulmonary defenses. NO production (protein expression, enzyme activity, end products, and exhaled NO measurements) was assessed in rats after cecal ligation and puncture to induce a mild peritonitis (leading to approximately 20% mortality rate). An early and sustained decrease in exhaled NO was found after peritonitis (from 1 to 72 h) compared with healthy rats [median (25th-75th percentile), 1.5 parts per billion (ppb) (1.2-1.7) vs. 4.0 ppb (3.6-4.3), P < 0.05], despite increased NO synthase-2 and unchanged NO synthase-3 protein expression in lung tissue. NO synthase-2 activity was decreased in lung tissue. Nitrites and nitrates in supernatants of isolated alveolar macrophages decreased after peritonitis compared with healthy rats, and an inhibitory experiment suggested arginase overactivity in alveolar macrophages bypassing the NO substrate. Administration of the NO synthase-2 inhibitor aminoguanidine to healthy animals reproduced the decreased neutrophil migration toward alveolar spaces that was observed after peritonitis, but L-arginine administration after peritonitis failed to correct the defect of neutrophil emigration despite increasing exhaled NO compared with D-arginine administration [4.8 (3.9-5.7) vs. 1.6 (1.3-1.7) ppb, respectively, P < 0.05]. In conclusion, the decrease in exhaled NO observed after mild peritonitis could serve as a marker for lung immunodepression.     

Temporal association of nitric oxide levels and airflow in asthma after whole lung allergen challenge.

Exhaled nitric oxide (NO) levels are high in asthmatic subjects and increase with exacerbations. We hypothesized that higher levels of NO observed during asthma exacerbations are due to increased synthesis of NO. Exhaled NO and peak flows were measured in 11 asthmatic and 9 healthy control subjects before and after experimental asthmatic response induced by whole lung allergen challenge. Baseline peak flows of asthmatics were significantly lower than controls and decreased significantly immediately after challenge (P = 0.004). NO was measured by collecting exhaled breaths without breath hold (NO0) and after a 15-s breath hold (NO15). The rate of NO accumulation over time [parts/billion per second (ppb/s)] was calculated by DeltaNO/Deltat = (NO15 - NO0)/15, where Delta denotes a change and t is time. The NO accumulation rates in asthmatic and control subjects were similar at baseline; however, NO accumulation at 24 h increased threefold from baseline in asthmatic compared with control subjects (asthmatic subjects, 0.6 +/- 0.2 ppb/s; control subjects, 0.2 +/- 0.1 ppb/s; P = 0.01). Our study suggests that increased NO during an asthma exacerbation is due to increased synthesis, perhaps by increased expression of NO synthases.     

Airway inflammation in nonasthmatic amateur runners

Elite athletes show a high prevalence of symptoms and signs of asthma, but no study has assessed the acute effects of endurance exercise on airway cells in nonasthmatic athletes. We measured exhaled nitric oxide (NO) and collected samples of induced sputum after 3% NaCl aerosol administration for 20 min in nonasthmatic middle-aged amateur runners after the Fourth Palermo International Marathon and 6--9 wk later (habitual training period) at baseline. After the marathon, exhaled NO (n = 9 subjects) was higher [27 +/- 9 parts/billion (ppb)] than at baseline (12 +/- 4 ppb; P < 0.0005). Polymorphonuclear neutrophil (PMN) counts in induced sputum were much higher in runners (91.2 +/- 3.6% of total cells postmarathon and 78.7 +/- 9.1% at baseline) than in sedentary control subjects (9.9 +/- 5.9%; P < 0.001). Expression of L-selectin and CD11b/CD18 in sputum PMNs was lower after the race than at baseline and inversely related to the amount of exhaled NO (r = -0.66 and -0.69, respectively; P < 0.05). Our data indicate that sputum PMNs are increased in nonasthmatic runners both after a marathon and at baseline and suggest that NO may modulate exercise-associated inflammatory airway changes.     

Assessment of exhaled gases in ventilated preterm infants

Hydrogen peroxide (H2O2) production in exhaled air was measured in ventilated preterm newborns at 5, 24 and 48 hours after delivery, using originally designed method of exhaled breath condensate (EBC) collection. H2O2 production in expired gas was 812+/-34 pmol/20 min during the first measurement and then declined to 389+/-21 at 24 hours and 259+/-26 pmol/20 min at 48 hours.     

Chromium status of full-term and preterm newborns

In order to obtain reference values from normal babies, Cr status of full-term newborns has been studied. Plasma and urine values were (mean±SEM) 0.7±0.1 μg/L and 0.9±0.3 μg/L, respectively, for the first month of life (n=19), and 0.6±0.1 μg/L and 0.8±0.2 μg/L for the second-to-third-month period (n=31). Premature newborns (gestational age 28–36 wk) were compared to these control values; concentrations were 0.9±0.1 μg/L and 1.1±0.2 μg/L for the first month (n=47), and 1.0±0.2 μg/L and 1.5±0.3 μg/L for the second to third months (n=27). For the whole group, there was a positive correlation between plasma and urine concentrations (p=0.0001); multiple regression analysis was performed between plasma levels and gestational age at birth (p=?0.002) and postnatal age (NS). Plasma levels of prematures and full terms were statistically different (p=0.03) only for the second- to third-month period. It is suggested that these high Cr levels result from high dietary intakes and/or high absorption rates.     

Increased Asymmetric Dimethylarginine in Severe Falciparum Malaria: Association with Impaired Nitric Oxide Bioavailability and Fatal Outcome

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is a predictor of mortality in critical illness. Severe malaria (SM) is associated with decreased NO bioavailability, but the contribution of ADMA to the pathogenesis of impaired NO bioavailability and adverse outcomes in malaria is unknown. In adults with and without falciparum malaria, we tested the hypotheses that plasma ADMA would be: 1) increased in proportion to disease severity, 2) associated with impaired vascular and pulmonary NO bioavailability and 3) independently associated with increased mortality. We assessed plasma dimethylarginines, exhaled NO concentrations and endothelial function in 49 patients with SM, 78 with moderately severe malaria (MSM) and 19 healthy controls (HC). Repeat ADMA and endothelial function measurements were performed in patients with SM. Multivariable regression was used to assess the effect of ADMA on mortality and NO bioavailability. Plasma ADMA was increased in SM patients (0.85 µM; 95% CI 0.74–0.96) compared to those with MSM (0.54 µM; 95%CI 0.5–0.56) and HCs (0.64 µM; 95%CI 0.58–0.70; p<0.001). ADMA was an independent predictor of mortality in SM patients with each micromolar elevation increasing the odds of death 18 fold (95% CI 2.0–181; p = 0.01). ADMA was independently associated with decreased exhaled NO (r_s = −0.31) and endothelial function (r_s = −0.32) in all malaria patients, and with reduced exhaled NO (r_s = −0.72) in those with SM. ADMA is increased in SM and associated with decreased vascular and pulmonary NO bioavailability. Inhibition of NOS by ADMA may contribute to increased mortality in severe malaria.     

Effects of various antioxidants on endotoxin-induced lung injury and gene expression: mRNA expressions of MnSOD, interleukin-1beta and iNOS

Antioxidants have been shown to be effective in attenuating acute lung injury. In this study, we determine the effects of various antioxidants by different mechanisms on the lipopolysaccharide (LPS)-induced changes. LPS was administered intravenously at a dose of 10 mg/kg to anesthetized rats. LPS induced a significant decrease in blood pressure (P < 0.01) and increased exhaled nitric oxide (NO) from 3.60+/-0.18 to 35.53+/-3.23 ppb (P < 0.01) during an observation period of 4 h. Plasma nitrate concentrations also increased from 0.61+/-0.06 to 1.54+/-0.22 micromol/l (P < 0.05). LPS-induced oxygen radical release from white blood cells isolated from rat peripheral blood also increased significantly (P < 0.001). After the experiment, the lung weight was obtained and lung tissues were taken for the determination of mRNA expression of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta) and manganese superoxide dismutase (MnSOD). Histological examination of the lungs was also performed. In the control group injected with saline solution, mRNA expressions of iNOS, IL-1beta, TNF-alpha and MnSOD were absent. Four hours after LPS administration, mRNA expressions of iNOS, IL-1beta, and MnSOD were significantly enhanced, but TNF-alpha was not discernibly expressed. LPS also caused a twofold increase in lung weight. Pathological examination revealed endothelial cell damage and interstitial edema. Various antioxidants were given 1 h after LPS administration. These agents include SOD, catalase (CAT), SOD + CAT or vitamin C (ascorbic acid). These antioxidants effectively reversed the systemic hypotension, reduced the quantity of exhaled NO and plasma nitrate concentration, and prevented acute lung injury. Administration of various antioxidants also significantly attenuated LPS-induced oxygen radical release by rat white blood cells. LPS induced mRNA expressions of MnSOD and iNOS were significantly depressed by these antioxidants. However, only SOD + CAT and vitamin C inhibited the mRNA expression of IL-1beta. These results suggest that oxygen radicals are responsible for LPS-induced lung injury. Antioxidants can attenuate the lung injury by inhibiting mRNA expressions of iNOS and IL-1beta.     

Assessment of exhaled nitric oxide kinetics in healthy infants.

Exhaled nitric oxide (Fe(NO)) measurements provide a noninvasive approach to the evaluation of airway inflammation. Flow-independent NO exchange parameters [airway NO transfer factor (D(NO)) and airway wall NO concentration (Cw(NO))] can be estimated from Fe(NO) measurements at low flows and may elucidate mechanisms of disturbances in NO exchange. We measured Fe(NO) in sedated infants by using an adaptation of a raised lung volume rapid thoracic compression technique that creates forced expiration through a mass-flow controller that lasts 5-10 s, at a constant preset flow. We measured Fe(NO) at expired flows of 50, 25, and 15 ml/s in five healthy infants (7-31 mo). Median Fe(NO) increased [24, 40, and 60 parts per billion (ppb)] with decreasing expiratory flows (50, 25, and 15 ml/s). Group median (range) for D(NO) and Cw(NO) were 12.7 (3.2-37) x 10(-3) nl. s(-1). ppb(-1) and 108.9 (49-385) ppb, respectively, similar to values reported in healthy adults. Exhaled NO is flow dependent; flow-independent parameters of exhaled NO kinetics can be assessed in infants and are similar to values described in adults.     

Plasma and exhaled breath condensate nitrite-nitrate level in relation to environmental exposures in adults in the EGEA study

This study evaluated the associations between biological markers in the nitrate-nitrite-NO pathway and four environmental exposures among subjects examined in the second survey (2003-2007) of the French Epidemiological study on Genetics and Environment of Asthma (EGEA). Total nitrite and nitrate (NO(2)(-) /NO(3)(-)) levels were measured both in plasma and in exhaled breath condensate (EBC) in 949 adults. Smoking, diet and exposure to chlorine products were assessed using standardized questionnaires. Exposure to air pollutants was estimated by using geostatistical models. All estimates were obtained with generalized estimating equations for linear regression models. Median levels of NO(2)(-)/NO(3)(-) were 36.3μM (1st-3rd quartile: 25.7, 51.1) in plasma and 2.0μmol/mg proteins (1st-3rd quartile 0.9, 3.9) in EBC. After adjustment for asthma, age, sex and menopausal status, plasma NO(2)(-)/NO(3)(-) level increased with leafy vegetable consumption (above versus below median=0.04 (95%CI: 0.001, 0.07)) and decreased in smokers (versus non/ex-smokers=-0.08 (95%CI: -0.11, -0.04). EBC NO(2)(-)/NO(3)(-) level decreased in smokers (-0.08 (95%CI: -0.16, -0.001)) and with exposure to ambient O(3) concentration (above versus below median=-0.10 (95%CI: -0.17, -0.03)). Cured meat, chlorine products, PM(10) and NO(2) concentrations were not associated with NO(2)(-)/NO(3)(-) levels. Results suggest that potential modifiable environmental and behavioral risk factors may modify NO(2)(-)/NO(3)(-) levels in plasma and EBC according to the route of exposure.     

Increase of nitrosative stress in patients with eosinophilic pneumonia

Background

Exhaled nitric oxide (NO) production is increased in asthma and reflects the degree of airway inflammation. The alveolar NO concentration (Calv) in interstitial pneumonia is reported to be increased. However, it remains unknown whether NO production is increased and nitrosative stress occurs in eosinophilic pneumonia (EP). We hypothesized that nitrosative stress markers including Calv, inducible type of NO synthase (iNOS), and 3-nitrotyrosine (3-NT), are upregulated in EP.

Methods

Exhaled NO including fractional exhaled NO (FE_NO) and Calv was measured in ten healthy subjects, 13 patients with idiopathic pulmonary fibrosis (IPF), and 13 patients with EP. iNOS expression and 3-NT formation were assessed by immunocytochemistory in BALf cells. The exhaled NO, lung function, and systemic inflammatory markers of the EP patients were investigated after corticosteroid treatment for 4 weeks.

Results

The Calv levels in the EP group (14.4 ± 2.0 ppb) were significantly higher than those in the healthy subjects (5.1 ± 0.6 ppb, p < 0.01) and the IPF groups (6.3 ± 0.6 ppb, p < 0.01) as well as the FE_NO and the corrected Calv levels (all p < 0.01). More iNOS and 3-NT positive cells were observed in the EP group compared to the healthy subject and IPF patient. The Calv levels had significant positive correlations with both iNOS (r = 0.858, p < 0.05) and 3-NT positive cells (r = 0.924, p < 0.01). Corticosteroid treatment significantly reduced both the FE_NO (p < 0.05) and the Calv levels (p < 0.01). The magnitude of reduction in the Calv levels had a significant positive correlation with the peripheral blood eosinophil counts (r = 0.802, p < 0.05).

Conclusions

These results suggested that excessive nitrosative stress occurred in EP and that Calv could be a marker of the disease activity.     

Plasma Cytokine Levels Fall in Preterm Newborn Infants on Nasal CPAP with Early Respiratory Distress

Introduction

Early nCPAP seems to prevent ventilator-induced lung injury in humans, although the pathophysiological mechanisms underlying this beneficial effect have not been clarified yet.

Objective

To evaluate plasma levels IL-1β, IL-6, IL-8, IL-10, and TNF-α immediately before the start of nCPAP and 2 hours later in preterm infants.

Methods

Prospective cohort including preterm infants with 28 to 35 weeks gestational age with moderate respiratory distress requiring nCPAP. Extreme preemies, newborns with malformations, congenital infections, sepsis, surfactant treatment, and receiving ventilatory support in the delivery room were excluded. Blood samples were collected right before and 2 hours after the start of nCPAP.

Results

23 preterm infants (birth weight 1851±403 grams; GA 32.3±1.7 weeks) were treated with nCPAP. IL-1β, IL-10, TNF-α levels were similar, IL-8 levels were reduced in 18/23 preterm infants and a significant decrease in IL-6 levels was observed after 2 hours of nCPAP. All newborns whose mothers received antenatal steroids had lower cytokine levels at the onset of nCPAP than those whose mothers didn’t receive it; this effect was not sustained after 2 hours of nCPAP.

Conclusion

Early use nCPAP is not associated with rising of plasma pro-inflammatory cytokines and it seems to be a less harmful respiratory strategy for preterm with moderate respiratory distress.     

Endogenous nitric oxide formation correlates negatively with circulating matrix metalloproteinase (MMP)-2 and MMP-9 levels in black subjects

Deficient formation of endogenous nitric oxide (NO) contributes to cardiovascular diseases, and this may be associated with increased circulating levels of matrix metalloproteinase-9 (MMP-9), as previously shown in white subjects. Because interethnic differences exist with respect to risk factors, prevalence, and severity of cardiovascular diseases, we designed this study to examine whether the circulating levels of nitrites (a marker of endogenous NO formation) are associated with the plasma levels of MMP-9 and MMP-2 in healthy black subjects. We studied 198 healthy subjects self-reported as blacks not taking any medications. Venous blood samples were collected and plasma and whole blood nitrite levels were measured using an ozone-based chemiluminescence assay. Plasma MMP-2 and MMP-9 levels were determined by gelatin zymography. We found a positive correlation between plasma MMP-9 and MMP-2 levels (P < 0.0001, rs = 0.556). Interestingly, we found a negative relationship between the plasma MMP-9 levels and the plasma or whole blood nitrites levels (P = 0.04, rs = -0.149; and P < 0.0001, rs = -0.349, respectively). In parallel, we found similar negative relationships between plasma MMP-2 levels and plasma or whole blood nitrites levels (P = 0.02, rs = -0.172; and P < 0.0001, rs = -0.454, respectively). This is the first study to show that endogenous nitric oxide formation correlates negatively with the circulating levels of both MMP-2 and MMP-9 in black subjects. Our findings suggest a mechanistic link between deficient NO formation and increased MMPs levels, which may promote cardiovascular diseases.     

Probing the impact of axial diffusion on nitric oxide exchange dynamics with heliox.

Exhaled nitric oxide (NO) is a potential noninvasive index of lung inflammation and is thought to arise from the alveolar and airway regions of the lungs. A two-compartment model has been used to describe NO exchange; however, the model neglects axial diffusion of NO in the gas phase, and recent theoretical studies suggest that this may introduce significant error. We used heliox (80% helium, 20% oxygen) as the insufflating gas to probe the impact of axial diffusion (molecular diffusivity of NO is increased 2.3-fold relative to air) in healthy adults (21-38 yr old, n = 9). Heliox decreased the plateau concentration of exhaled NO by 45% (exhalation flow rate of 50 ml/s). In addition, the total mass of NO exhaled in phase I and II after a 20-s breath hold was reduced by 36%. A single-path trumpet model that considers axial diffusion predicts a 50% increase in the maximum airway flux of NO and a near-zero alveolar concentration (Ca(NO)) and source. Furthermore, when NO elimination is plotted vs. constant exhalation flow rate (range 50-500 ml/s), the slope has been previously interpreted as a nonzero Ca(NO) (range 1-5 ppb); however, the trumpet model predicts a positive slope of 0.4-2.1 ppb despite a zero Ca(NO) because of a diminishing impact of axial diffusion as flow rate increases. We conclude that axial diffusion leads to a significant backdiffusion of NO from the airways to the alveolar region that significantly impacts the partitioning of airway and alveolar contributions to exhaled NO.     

Microscopic modeling of NO and S-nitrosoglutathione kinetics and transport in human airways.

Nitric oxide (NO) appears in the exhaled breath and is elevated in inflammatory diseases. We developed a steady-state mathematical model of the bronchial mucosa for normal small and large airways to understand NO and S-nitrosoglutathione (GSNO) kinetics and transport using data from the existing literature. Our model predicts that mean steady-state NO and GSNO concentrations for large airways (generation 1) are 2.68 nM and 113 pM, respectively, in the epithelial cells and 0.11 nM (approximately 66 ppb) and 507 nM in the mucus. For small airways (generation 15), the mean concentrations of NO and GSNO, respectively, are 0.26 nM and 21 pM in the epithelial cells and 0.02 nM (approximately 12 ppb) and 132 nM in the mucus. The concentrations in the mucus compare favorably to experimentally measured values. We conclude that 1) the majority of free NO in the mucus, and thus exhaled NO, is due to diffusion of free NO from the epithelial cell and 2) the heterogeneous airway contribution to exhaled NO is due to heterogeneous airway geometries, such as epithelium and mucus thickness.     

Enhanced nitric oxide production associated with airway hyporesponsiveness in the absence of IL-10

Interleukin (IL)-10 is an anti-inflammatory cytokine implicated in the regulation of airway inflammation in asthma. Among other activities, IL-10 suppresses production of nitric oxide (NO); consequently, its absence may permit increased NO production, which can affect airway smooth muscle contractility. Therefore, we investigated airway reactivity (AR) in response to methacholine (MCh) in IL-10 knockout (-/-) mice compared with wild-type C57BL/6 (C57) mice, in which airway NO production was measured as exhaled NO (E(NO)), and NO production was altered with administration of either NO synthase (NOS)-specific inhibitors or recombinant murine (rm)IL-10. AR, measured as enhanced pause in vivo, and tracheal ring tension in vitro were lower in IL-10(-/-) mice by 25-50%, which was associated with elevated E(NO) levels (13 vs. 7 ppb). Administration of NOS inhibitors N(G)-nitro-L-arginine methyl ester (8 mg/kg ip) or L-N(6)-(1-iminoethyl)-lysine (3 mg/kg ip) to IL-10(-/-) mice decreased E(NO) by an average of 50%, which was associated with increased AR, to levels similar to C57 mice. E(NO) in IL-10(-/-) mice decreased in a dose-dependent fashion in response to administered rmIL-10, to levels similar to C57 mice (7 ppb), which was associated with a 30% increment in AR. Thus increased NO production in the absence of IL-10, decreased AR, which was reversed with inhibition of NO, either by inhibition of NOS, or with reconstitution of IL-10. These findings suggest that airway NO production can modulate airway smooth muscle contractility, resulting in airway hyporesponsiveness when IL-10 is absent.