Nitric oxide and related enzymes in asthma: relation to severity, enzyme function and inflammation

Abstract

Background Exhaled nitric oxide (FeNO) associates with asthma and eosinophilic inflammation. However, relationships between nitric oxide synthases, arginase, FeNO, asthma severity and inflammation remain poorly understood. Objectives To determine the relationships of iNOS expression/activation and arginase 2 expression with asthma severity, FeNO, nitrotyrosine (NT) and eosinophilic inflammation. Methods Bronchial brushings and sputum were obtained from 25 Normal Controls, 8 Mild/no inhaled corticosteroids (ICS), 16 Mild-Moderate/with ICS and 35 Severe Asthmatics. FeNO was measured the same day by ATS/ERS standards. iNOS, Arginase2 mRNA/protein and NT protein were measured in lysates from bronchial brushings by quantitative real time PCR and Western Blot. Induced sputum differentials were obtained. Results Severe asthma was associated with the highest levels of iNOS protein and mRNA, although the index of iNOS mRNA to arginase2 mRNA most strongly differentiated severe from milder asthma. When evaluating NO-related enzyme functionality, iNOS mRNA/protein expression both strongly predicted FeNO (r=0.61, p<0.0001 for both). Only iNOS protein predicted NT levels (r=0.48, p=0.003) with the strongest relationship in severe asthma (r=0.61, p=0.009). iNOS protein, FeNO and NT all correlated with sputum eosinophils, but the relationships were again strongest in severe asthma. Controlling for arginase 2 mRNA/protein did not impact any functional outcome. Conclusions and Clinical Relevance These data suggest that while iNOS expression from epithelial brushings is highest in severe asthma, factors controlling arginase2 mRNA expression significantly improve differentiation of severity. In contrast, functionality of the NO pathway as measured by FeNO, NT and eosinophilic inflammation, is strongly associated with iNOS expression alone, particularly in severe asthma.

International ERS/ATS guidelines on definition, evaluation and treatment of severe asthma

“…Higher FeNO values, perhaps due to the higher reported inducible nitric oxide synthase expression in severe asthmatic epithelial cells, have been associated with a more exacerbation prone phenotype in severe asthma, as well as more rapid decline in FEV1 [76,[91][92][93]. In addition, higher levels of oxidative stress have been associated with a reduction in superoxide dismutase and s-nitrosothiol depletion [94,95].…”

Eosinophil-Associated Lung Diseases. A Cry for Surfactant Proteins A and D Help?

“…In addition, reactive oxygen and nitrogen species may also affect posttranslational modifications of SP-D that alter its structure and function at sites of inflammation (39,113). For example, NO, produced locally by airway epithelial cells and increased in asthma (114), has been shown to S-nitrosylate two free Cys thiols in the N-terminus of dodecameric SP-D (Cys- [15][16][17][18][19][20] and to affect dissociation into SP-D trimers (115). Consequences of this structural perturbation include the activation of SP-D proinflammatory chemoattractant function and the loss of control TLR4 blockade (39).…”

Gene Expression in Relation to Exhaled Nitric Oxide Identifies Novel Asthma Phenotypes with Unique Biomolecular Pathways

“…Fractional exhaled nitric oxide (FE NO ), an asthma biomarker that associates with atopy and eosinophilia (6,13), is strongly induced by type 2 cytokines in vitro. Its inhibition in vivo by biologic therapies targeted toward IL-4 and -13 confirms its association with this immune pathway (14)(15)(16)(17).…”