Elsevier

Free Radical Biology and Medicine

Volume 33, Issue 10, 15 November 2002, Pages 1403-1408
Free Radical Biology and Medicine

Original contribution
Ozone-induced increase in exhaled 8-isoprostane in healthy subjects is resistant to inhaled budesonide

https://doi.org/10.1016/S0891-5849(02)01084-5Get rights and content

Abstract

The aim of this study was to quantify lung oxidant stress after short-term ozone exposure as reflected by 8-isoprostane concentrations in exhaled breath condensate (EBC) and to investigate the effects of inhaled budesonide on this response. 8-Isoprostane is a prostaglandin-F isomer that is formed in vivo by free radical-catalyzed peroxidation of arachidonic acid. EBC is a noninvasive method to collect airway secretions. We undertook a double-blind, randomized, placebo-controlled, crossover study with inhaled budesonide (800 μg) or placebo twice daily for 2 weeks prior to ozone exposure (400 parts per billion) for 2 h in nine healthy nonsmokers. Exhaled 8-isoprostane was measured by an enzyme immunoassay. 8-Isoprostane was increased 4 h after ozone exposure compared to pre-exposure values in both placebo (36.9 ± 3.9 pg/ml, mean ± SEM, vs. 16.9 ± 0.7 pg/ml; p < .001) and budesonide groups (33.4 ± 2.6 pg/ml vs. 15.8 ± 0.3 pg/ml; p < .001). Pretreatment with budesonide did not affect the increases in 8-isoprostane (mean differences 3.4 pg/ml, 95% CI −8.9 to 15.7, p = .54). Short-term ozone exposure causes acute increase in lung oxidative stress as reflected by exhaled 8-isoprostane. This increase is resistant to pretreatment with a high dose of inhaled budesonide.

Introduction

Ozone exposure in humans causes airway inflammation [1]. This response is characterized by decreased lung function [2], increased bronchial reactivity to methacholine [3], and increases in inflammatory cells and markers in both bronchoalveolar (BAL) fluid [4] and induced sputum [5]. We have recently demonstrated that lung inflammation induced by acute ozone exposure in healthy volunteers is not affected by pretreatment with budesonide, an inhaled corticosteroid [3]. We found decreased lung function, increased methacholine reactivity, and increased inflammatory markers in sputum (neutrophils, myoloperoxydase). There was no change in the exhaled markers such as nitric oxide (NO), carbon monoxide (CO), and nitrite [3].

Oxidative stress, which is an important pathogenetic component of lung inflammation, is also increased after ozone exposure in healthy volunteers as reflected by increased 8-isoprostane in airway lavage [1]. Isoprostanes are prostaglandin-like compounds produced by free radical peroxidation of arachidonic acid [6]. Measurements of these compounds in exhaled breath condensate (EBC), a new noninvasive method to sample secretions from the airways [7], has several advantages over other quantitative biomarkers of oxidant stress [8]. Isoprostanes (i) are chemically stable; (ii) are formed in vivo; (iii) are specific for lipid peroxidation, which is an important step in oxidative stress; (iv) exert biological activity, which may be relevant to the pathophysiology of lung diseases; (v) are used to define the clinical pharmacology of antioxidants; and, (vi) are measurable in EBC, which is likely to reflect oxidative stress in the lung [9].

We have previously shown that 8-isoprostane, a member of the F2 isoprostane class, is increased in EBC of patients with inflammatory airway diseases, such as asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and in BAL fluid in patients with interstitial lung diseases 9, 10, 11, 12. Measurement of 8-isoprostane in EBC is potentially useful for noninvasive monitoring of ozone-induced oxidative stress in the lung. However, the effects of inhaled corticosteroids on 8-isoprostane are not clear. There is only one study showing that beclomethasone, an inhaled corticosteroid, reduces the 8-isoprostane increase in BAL in patients with asthma after antigen challenge [13]. However, in a previous study, we were unable to demonstrate any effect of pretreatment with inhaled budesonide on ozone-induced increase in inflammatory markers such as neutrophils and myeloperoxidase in sputum in healthy subjects [3].

The aim of this study was to investigate if oxidant stress, as reflected by exhaled 8-isoprostane, is affected by short-term ozone exposure and the effect of inhaled budesonide on free radical production after ozone exposure.

Section snippets

Subjects characteristics

Nine healthy subjects were studied (four men and five women; age: 30 ± 2.8 years, mean ± SEM). These subjects were previously enrolled in another study [3]. All had normal lung function (forced expiratory volume in 1 s [FEV1] 95.1 ± 3.2% predicted value, mean ± SEM), normal bronchial reactivity (screening provocative concentration of methacholine causing a 20% reduction in FEV1 [PC20] > 64 mg/ml), and were nonatopic on skin prick testing to common aeroallergens (cat, grass, pollen,

Exhaled 8-isoprostane

There was no difference between pre-exposure concentrations of exhaled 8-isoprostane in the two study groups (placebo: 16.9 ± 0.7 pg/ml; budesonide: 15.8 ± 0.3 pg/ml, p = .16). Compared with baseline values (15.8 ± 1.2 pg/ml, placebo and 15.3 ± 1.3 pg/ml, budesonide), there was no change after placebo (16.9 ± 0.7 pg/ml, p = .43) or budesonide treatment (15.8 ± 0.3 pg/ml, p = .71). 8-Isoprostane concentrations in EBC were increased 4 h after ozone exposure compared to pre-exposure values in both

Discussion

8-Isoprostane is formed in vivo by free radical peroxidation of arachidonic acid [6]. Measurement of this compound in biological fluid may provide a quantitative index of in vivo oxidative stress, which is an important component of airway inflammation [8].

In this study, we showed that short-term exposure to ozone causes an increase in lung oxidative stress that lasts up to 4 h as reflected by 8-isoprostane concentrations in EBC of healthy volunteers. These results are consistent with previous

Abbreviations

  • BAL—bronchoalveolar lavage

  • CI—confidence intervals

  • CO—carbon monoxide

  • EBC—exhaled breath condensate

  • EIA—enzyme immunoassay

  • FEV1—forced expiratory volume in 1 s

  • FVC—forced vital capacity

  • NO—nitric oxide

  • PC20—provocative concentration that causes 20% decrease in FEV1

  • ppb—parts per billion

  • SEM—standard error of the mean

Acknowledgements

This work was funded by Imperial College, National Heart and Lung Institute, London, England. This work was performed at Imperial College, School of Medicine at the National Heart and Lung Institute, Department of Thoracic Medicine, Dovehouse Street, London, England.

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