NO chemical events in the human airway during the immediate and late antigen-induced asthmatic response

Abstract

A wealth of evidence supports increased NO (NO.) in asthma, but its roles are unknown. To investigate how NO participates in inflammatory airway events in asthma, we measured NO. and NO. chemical reaction products [nitrite, nitrate, S-nitrosothiols (SNO), and nitrotyrosine] before, immediately and 48 h after bronchoscopic antigen (Ag) challenge of the peripheral airways in atopic asthmatic individuals and nonatopic healthy controls. Strikingly, NO(3)(-) was the only NO. derivative to increase during the immediate Ag-induced asthmatic response and continued to increase over 2-fold at 48 h after Ag challenge in contrast to controls [P < 0.05]. NO(2)(-) was not affected by Ag challenge at 10 min or 48 h after Ag challenge. Although SNO was not detectable in asthmatic airways at baseline or immediately after Ag, SNO increased during the late response to levels found in healthy controls. A model of NO. dynamics derived from the current findings predicts that NO. may have harmful effects through formation of peroxynitrite, but also subserves an antioxidant role by consuming reactive oxygen species during the immediate asthmatic response, whereas nitrosylation during the late asthmatic response generates SNO, safe reservoirs for removal of toxic NO. derivatives.

Figures

Figure 1

An asthmatic individual with higher NO⋅ plateau in intrapulmonary gases than a healthy control individual at Baseline before Ag challenge. At 10 min after Ag challenge (Ag 10 min), NO⋅ plateau levels are similar to baseline levels, but by 48 h after Ag challenge (Ag 48 h), the NO⋅ plateau in the asthmatic airway gases is much higher than plateau levels at baseline. In contrast, the nonatopic healthy control had no increase in plateau NO⋅ in intrapulmonary gases. Each point represents a single NO⋅ determination in gases continually sampled from the lower airway at bronchoscopy at intervals of 0.05 sec.

Figure 2

NO metabolites in BAL fluid from asthmatic and control airways before (0 min), and 10 min or 48 h after segmental Ag challenge. NO in asthmatic or control BAL fluid did not change significantly with Ag challenge from baseline (all comparisons. P > 0.5). NO increases at 10 min and 48 h after Ag challenge in asthmatics, whereas NO did not change in control airways. SNO were undetectable in the asthmatic airway at baseline and 10 min after Ag challenge but increased at 48 h after Ag challenge.

Figure 3

Nitrotyrosine immunostaining of asthmatic and healthy control bronchial mucosa. (A) Asthmatic bronchial mucosa has marked increase in goblet cells and thickened basement membrane. The epithelial cells stain prominently for nitrotyrosine (red staining); red, arrow; g, goblet cell. (B) At 48 h after Ag challenge, epithelial cells are sloughing from the thickened basement membrane (bm), but the cells remaining show positivity for nitrotyrosine. (C) Healthy control bronchial mucosa shows typical pseudostratified columnar epithelium, with red staining present in apical portions of cells (×40; hematoxylin counterstaining).

Figure 4

Model of NO⋅ reactions in the lung during an Ag-induced asthmatic response.