Peroxynitrite, nitrogen dioxide, and other reactive nitrogen species (RNS) that are formed in the reaction of nitric oxide (NO) with superoxide anion, and in peroxidase-dependent mechanisms, have a potent inflammatory action. These molecules may therefore increase in number and have a role in inflammatory airway diseases. In the present study, we quantified RNS using immunostaining of nitrotyrosine and inducible NO synthase (iNOS) in airway inflammatory cells obtained by the induced sputum technique, and also quantified the exhaled NO concentration in subjects with chronic obstructive pulmonary disease (COPD), subjects with asthma, and healthy subjects (HS). Immunoreactivity for iNOS observed in the airway inflammatory cells was significantly and similarly higher in subjects with COPD and asthma than in HS, although exhaled NO levels were increased only in subjects with asthma. Inflammatory cells showed obvious nitrotyrosine immunoreactivity in subjects with COPD and to a lesser extent in those with asthma, but not in HS. There was a significant negative correlation between the percent predicted values of FEV(1) and the amount of nitrotyrosine formation in subjects with COPD, but not in those with asthma and HS. These results suggest that: (1) RNS may be involved in the pathobiology of the airway inflammatory and obstructive process in COPD; and (2) NO produced in the airways, presumably via iNOS, is consumed by its reaction with superoxide anion and/or peroxidase-dependent mechanisms.

We investigated the role of peroxynitrite, which is formed by a rapid reaction between nitric oxide (NO) and superoxide anion (O(2)(-)), in the airway microvascular hyperpermeability during the late allergic response (LAR) in sensitized guinea pigs in vivo. The occurrence of LAR was assessed as a 100% increase in the transpulmonary pressure, which was monitored by the esophageal catheter technique. Airway microvascular permeability was assessed by Monastral blue dye trapping between the endothelium using an image analyzer. In the LAR phase (4 to 6 h after antigen inhalation), microvascular hyperpermeability and eosinophil infiltration within the airway wall were observed. NO production and xanthine oxidase (XO)/xanthine dehydrogenase activity, which are responsible for O(2)(-) production, were enhanced during the LAR. Peroxynitrite formation assessed by nitrotyrosine immunostaining was also exaggerated at that time. The microvascular hyperpermeability during the LAR was largely reduced by NO synthase inhibitor (L-NAME, 72.7% inhibition; p < 0.05), XO inhibitor (AHPP, 60.8% inhibition; p < 0. 05) and peroxynitrite scavenger (ebselen, 81.0% inhibition; p < 0. 05). L-NAME had a small but significant inhibitory effect on airway eosinophil accumulation, but AHPP and ebselen had no effect. These results suggest that excessive production of O(2)(-) and NO occurs in the LAR. These two molecules appear to cause airway microvascular hyperpermeability via peroxynitrite formation.

Reactive nitrogen species (RNS) have been reported to be involved in the inflammatory process in chronic obstructive pulmonary disease (COPD). However, there are no studies on the modulation of RNS in COPD. It was hypothesised that inhibition of xanthine oxidase (XO) might decrease RNS production in COPD airways through the suppression of superoxide anion production.Ten COPD and six healthy subjects participated in the study. The XO inhibitor allopurinol (300 mg?day -1 p.o. for 4 weeks) was administered to COPD patients. RNS production in the airway was assessed by 3-nitrotyrosine immunoreactivity and enzymic activity of XO in induced sputum as well as by exhaled nitric oxide (eNO) concentration.XO activity in the airway was significantly elevated in COPD compared with healthy subjects. Allopurinol administration to COPD subjects significantly decreased XO activity and nitrotyrosine formation. In contrast, eNO concentration was significantly increased by allopurinol administration.These results suggest that oral administration of the xanthine oxidase inhibitor allopurinol reduces airway reactive nitrogen species production in chronic obstructive pulmonary disease subjects. This intervention may be useful in the future management of chronic obstructive pulmonary disease. Eur Respir J 2003; 22: 457-461.

SummaryInterleukin (IL)-18, which is produced by activated monocytes/macrophages and airway epithelial cells, is suggested to contribute to the pathophysiology of asthma by modulating airway inflammation. However, the involvement of IL-18 on modulating chronic airway inflammation and airway remodelling, which are characterized in a refractory asthma model exposed to long-term antigen, has not been investigated sufficiently. We examined the role of IL-18 in chronic airway inflammation and airway remodelling by long-term antigen exposure. IL-18-deficient and C57BL/6-wild-type mice were sensitized by ovalbumin (OVA) and were then exposed to aerosolized OVA twice a week for 12 weeks. We assessed airway inflammation by assessing the infiltration of cells into the airspace and lung tissues, and airway remodelling by airway mucus expression, peribronchial fibrosis and smooth muscle thickness. In IL-18-deficient mice, when exposed to OVA, the total cells and neutrophils of the bronchoalveolar lavage fluid (BALF) were diminished, as were the number of infiltrated cells in the lung tissues. IL-18-deficient mice exposed to OVA after 12 weeks showed significantly decreased levels of interferon (IFN)-g, IL-13 and transforming growth factor (TGF)-b1 in the BALF. The airway hyperresponsiveness to acetyl-b-methacholine chloride was inhibited in IL-18-deficient mice in comparison with wild-type mice. In addition, IL-18-deficient mice exposed to OVA had fewer significant features of airway remodelling. These findings suggest that IL-18 may enhance chronic airway inflammation and airway remodelling through the production of IFN-g, IL-13 and TGF-b1 in the OVA-induced asthma mouse model.