Airway glutathione homeostasis is altered in children with severe asthma: evidence for oxidant stress

Abstract

Background: Severe asthma is characterized by persistent airway inflammation and increased formation of reactive oxygen species.

Objectives: Glutathione (GSH) is an important antioxidant in the epithelial lining fluid (ELF). We hypothesized that airway GSH homeostasis was altered in children with severe asthma and was characterized by decreased GSH and increased glutathione disulfide (GSSG) concentrations.

Methods: Bronchoalveolar lavage was obtained from 65 children with severe asthma, including 35 children with baseline airway obstruction evidenced by FEV(1) <80%. Control data were obtained from 6 children with psychogenic (habit) cough or vocal cord dysfunction undergoing diagnostic bronchoscopy and 35 healthy adult controls. GSH, GSSG, and other determinants of airway oxidative stress including glutathione S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPx), malondialdehyde, 8-isoprostane, and H(2)O(2) were measured in the ELF. The ELF redox potential was calculated from GSH and GSSG by using the Nernst equation.

Results: Compared with controls, subjects with severe asthma had lower airway GSH with increased GSSG despite no differences in GST, GR, and GPx activities between groups. This was accompanied by increased malondialdehyde, 8-isoprostane, and H(2)O(2) concentrations in the ELF. GSH oxidation was most apparent in subjects with severe asthma with airway obstruction and was supported by an upward shift in the ELF GSH redox potential.

Conclusion: Children with severe asthma have increased biomarkers of oxidant stress in the ELF that are associated with increased formation of GSSG and a shift in the GSH redox potential toward the more oxidized state.

FIG 1

Diagram of airway glutathione homeostasis. ROOH and ROH represent organic hydroperoxides.

FIG 2

Airway glutathione characteristics. A, GSH. B, GSSG. C, % GSSG. D, The redox potential (E_h) of the GSH/GSSG pair in the ELF. Data represent the means ± SEMs per mL of ELF with AC = adult control (n = 31), PC = pediatric control (n = 6), AO− = severe asthma without airway obstruction (n = 31), and AO+ = severe asthma with airway obstruction (n = 25). *P < .01 vs adult controls; †P < .05 vs pediatric controls.

FIG 3

Airway biomarkers of oxidant stress. A, Malondialdehyde. B, 8-isoprostane. C, H₂O₂ concentrations in the ELF. Data represent the means ± SEMs per mL of ELF with AC = adult controls, PC = pediatric controls, AO− = severe asthma without airway obstruction, and AO+ = severe asthma with airway obstruction. *P < .01 vs adult controls; †P < .05 vs pediatric controls; ‡P < .05 vs subjects with severe asthma without airway obstruction.