Ozone-induced airway hyperresponsiveness: role of superoxide anions, NEP, and BK receptors

Abstract

We investigated the role of reactive oxygen species in ozone-induced airway hyperresponsiveness (AHR) in Brown Norway rats. Airway responsiveness to inhaled acetylcholine (ACh) and bradykinin (BK) and inflammatory cell recruitment in bronchoalveolar lavage fluid (BALF) were measured in vivo. Neutral endopeptidase (NEP) activity assay and measurement of BK-receptor binding sites in Brown Norway rat lungs were carried out in vitro. Apocynin (5 mg/kg), an inhibitor of superoxide anion-generating NADPH oxidase, was administered perorally 30 min before a 3- or 6-h exposure to 3 ppm of ozone, and the animals were studied 18-24 h postexposure. Ozone induced increases in airway responsiveness to ACh and BK and in neutrophil counts in BALF. Apocynin inhibited the increase in airway responsiveness to BK but not to ACh without affecting the neutrophil counts in BALF. The antioxidants allopurinol and deferoxamine prevented ozone-induced AHR to both ACh and BK but did not reduce neutrophil counts. To further examine the mechanisms of ozone-induced AHR to BK, we measured NEP activity and the density of BK receptors in vitro after ozone exposure. Ozone exposure had no significant effect either on NEP activity or on the affinity and the number of BK receptors in lungs from rats treated with or without apocynin. We conclude that superoxide anions released from inflammatory cells in the airway may be involved in ozone-induced AHR. Inactivation of NEP or upregulation of BK receptors do not appear to be involved, but the possibility of localized changes cannot be excluded.

Nonhematopoietic NADPH oxidase regulation of lung eosinophilia and airway hyperresponsiveness in experimentally induced asthma

“…(59). In addition, ozone-induced AHR is blocked by apocynin, an inhibitor of NADPH oxidase, but, as NADPH oxidase functions in leukocytes and nonhematopoietic cells, the source of NADPH oxidase contributing to this AHR was not determined (61). ROS can also be generated by NADPH oxidases in type II epithelial cells in response to PMA or bacteria (66).…”

“…Whether NADPH oxidase in nonhematopoietic cells is involved in VCAM-1-dependent eosinophil migration has not been demonstrated. We suggest that, in addition to ROS modulation of lung tissue responses (11,43,59,61,66), ROS are required for VCAM-1 signals and thus VCAM-1-dependent infiltration of eosinophils into the lung in response to ovalbumin (OVA) inhalation. We have reported that when we elevate the levels of the antioxidant bilirubin, it inhibits OVA-induced lung eosinophilia and blocks VCAM-1 signaling in vitro (30).…”

Ozone induction of cytokine‐induced neutrophil chemoattractant (CINC) and nuclear factor‐κb in rat lung: inhibition by corticosteroids

“…Lavaged lungs were then used for mRNA extraction and electrophoretic mobility shift assays. The retrieval and differential cell counts were performed as previously described [5].…”

“…Exposure of animals to ozone induces infiltration of neutrophils into the airways with an increase in airway's responsiveness [5,6]. Ozone exposure also induces the expression of the chemokine MIP-2 in mouse and rat lung [7,8].…”

Alveolar Epithelial Cells Secrete Chemokines in Response to IL-1β and Lipopolysaccharide but Not to Ozone

“…Alveolar and airway epithelial cells are among the first cells to come in contact with inhaled ozone and thus constitute one of the primary targets for ozone toxicity. Exposure to ozone induces acute inflammation and a neutrophil influx in vivo (4)(5)(6). In humans and monkeys, the neutrophil influx has been suggested to be due to secretion of IL-8 (7)(8)(9).…”