Exhaled nitric oxide levels and airway responsiveness to adenosine 5'-monophosphate in subjects with nasal polyposis

Increased phosphorylation of eNOS in nasal polyps of chronic rhinosinusitis patients can be diminished by 1,8-cineol

INTRODUCTION

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a significant health problem, but the pathogenesis remains unclear to date. Nitric oxide (NO) has known airway modulating functions. Therefore, we investigated nitric oxide production to determine the role of eNOS in nasal polyps, with additional analysis of the effect of the monoterpene oxide 1,8-cineol on the possible regulation of eNOS signaling and thus NO production.

METHODS

We determined eNOS expression, as well as regulatory and effector proteins like NOSTRIN and CASP8, using whole genome microarray, immunohistochemistry and western blot. To evaluate the influence of 1,8-cineol on eNOS signaling, we examined tissue samples of nasal polyps of patients with CRSwNP incubated with 100 μM 1,8-cineol using quantitative real-time PCR, western blot and phosphorylation arrays.

RESULTS

Microarray analysis revealed an increased gene expression of eNOS (1.40-fold) as well as a decreased gene expression of NOSTRIN (0.53-fold) and CASP8 (0.44-fold) in nasal polyps. At the protein level, we detected 2.3-fold higher protein expression of eNOS and significant higher phosphorylation levels of eNOS in nasal polyps (19.7-fold, p ≤ 0.001) compared to inferior turbinates. Additionally, 1,8-cineol did not influence NOSTRIN and CASP8, but decreased the eNOS phosphorylation significantly (p ≤ 0.05).

DISCUSSION

Our study demonstrated for the first time that nasal polyps exhibit an increased phosphorylation of eNOS, which could be important for vascular permeability and the associated edema and elevated inflammation. Additionally, we detected that 1,8-cineol affects the eNOS phosphorylation significantly and thus its activation. This could be important to handle the elevated inflammation and edema formation by regulating the vascular permeability.

Maximal response plateau to adenosine 5'-monophosphate in asthma. Relationship with the response to methacholine, exhaled nitric oxide, and exhaled breath condensate pH

BACKGROUND

No information is available on the plateau in response to adenosine 5'-monophosphate(AMP). The aims of the present study were (1) to determine whether plateau can be detected with AMP and the relation with the plateau in response to methacholine, and (2) to identify the relation between the plateau and indirect markers of airway inflammation, such as exhaled nitric oxide (ENO) and exhaled breath condensate (EBC) pH.

METHODS

Airway responsiveness to high concentrations of methacholine and AMP, ENO levels, and EBC pH values were obtained in 31 subjects with well-controlled asthma. Concentration-response curves were characterized by their concentration of agonist that produces a decrease in FEV(1) of 20% and, if possible, by the level of plateau.

RESULTS

Although the prevalence of plateau with methacholine (48%) and AMP (58%) was similar, the two challenges did not identify plateau in exactly the same individuals. In 14 subjects who showed plateau with both bronchoconstrictor agents, the mean plateau level for methacholine was 26.0% (95% confidence interval [CI], 21.3 to 30.8), compared with 16.5% (95% CI, 12.2 to 20.8; p < 0.0001) for AMP. Both ENO and EBC pH values were similar in subjects with plateau and in those without plateau.

CONCLUSIONS

In well-controlled asthmatics, the plateau in response to AMP can be identified at a milder degree of obstruction than the plateau in response to methacholine, but the two agonists are not identifying the same airway abnormalities. Furthermore, if ENO and EBC pH are markers of inflammation, the determination of the presence or level of plateau is not a reliable method to identify airway inflammation in asthma.

AMP challenge induces a decrease in FE(NO) in asthmatic subjects modulated by nedocromil

BACKGROUND

Allergen challenge results in an immediate reduction in exhaled nitric oxide (FE(NO)) followed by a long-term increase. To study mast cell activation in relation to nitric oxide (NO), the study investigated the effect of inhaled adenosine monophosphate (AMP) as a mast cell activator and mast cell stabilizer - nedocromil sodium - on FE(NO). The NO synthase (NOS) iso-enzyme involved was studied by the NOS inhibitor aminoguanidine.

MATERIALS AND METHODS

A double-blind, placebo-controlled, cross-over study was performed in two parts. Part I: eight atopic asthmatic subjects inhaled nedocromil or placebo before the AMP challenge. Spirometry and FE(NO) were measured at intervals over a 24-h period. Part II: seven subjects inhaled aminoguanidine before an identical protocol was used, as in Part I.

RESULTS

Part I: AMP challenge caused a significant decrease from baseline FE(NO)[placebo, 28.9 (20.3-37.4)%, P < 0.002 and nedocromil, 20.9 (8.2-33.6)%, P < 0.01]. Nedocromil gave partial protection against this decrease in FE(NO). The time-FE(NO) curve (AUC(0-24)) differed significantly between nedocromil and placebo: 2.7% (-3.6 to -9) vs. -6.6% (-12 to -1.3) FE(NO) changes h(-1), P < 0.002, respectively. Nedocromil protected against AMP-induced bronchoconstriction (AMP PC(20)) [nedocromil 182 (72.5-291) mg mL(-1) vs. placebo 21.7 (10.7-33) mg mL(-1), P < 0.002]. Part II: nebulized aminoguanidine resulted in a significant reduction in FE(NO) from baseline and was greater than after AMP alone (P = 0.006). Nedocromil increased AMP PC(20), but no longer protected against the late decrease in FE(NO).

CONCLUSIONS

The AMP challenge caused a reduction in FE(NO) as a result of prior treatment with nedocromil. Aminoguanidine abolished the nedocromil-induced protection on the late reduction in FE(NO), but not on AMP PC(20). Inducible NOS was implicated in the late FE(NO) decrease after the AMP challenge.