Reactive oxygen species and
reactive nitrogen species produced by epithelial and inflammatory cells are key mediators of the chronic airway
inflammation of
asthma. Detection of
3-nitrotyrosine in the asthmatic lung confirms the presence of increased reactive
oxygen and
nitrogen species, but the lack of identification of modified
proteins has hindered an understanding of the potential mechanistic contributions of nitration/oxidation to airway
inflammation. In this study, we applied a proteomic approach, using
nitrotyrosine as a marker, to evaluate the oxidation of
proteins in the
allergen-induced murine model of
asthma. Over 30 different
proteins were targets of nitration following
allergen challenge, including the
antioxidant enzyme catalase. Oxidative modification and loss of
catalase enzyme function were seen in this model. Subsequent investigation of human bronchoalveolar lavage fluid revealed that
catalase activity was reduced in
asthma by up to 50% relative to healthy controls. Analysis of
catalase isolated from asthmatic airway epithelial cells revealed increased amounts of several
protein oxidation markers, including chloro- and
nitrotyrosine, linking oxidative modification to the reduced activity in vivo. Parallel in vitro studies using reactive chlorinating species revealed that
catalase inactivation is accompanied by the oxidation of a specific
cysteine (Cys(377)). Taken together, these studies provide evidence of multiple ongoing and profound oxidative reactions in asthmatic airways, with one early downstream consequence being
catalase inactivation. Loss of
catalase activity likely amplifies oxidative stress, contributing to the chronic inflammatory state of the asthmatic airway.