NADPH:
quinone oxidoreductase 1 (NQO1) is recognized as a major susceptibility gene for
ozone-induced pulmonary toxicity. In the absence of NQO1 as can occur by genetic mutation, the human airway is protected from harmful effects of
ozone. We recently reported that NQO1-null mice are protected from
airway hyperresponsiveness and
pulmonary inflammation following
ozone exposure. However, NQO1 regenerates intracellular
antioxidants and therefore should protect the individual from oxidative stress. To explain this paradox, we tested whether in the absence of NQO1
ozone exposure results in increased generation of A(2)-isoprostane, a
cyclopentenone isoprostane that blunts
inflammation. Using GC-MS, we found that NQO1-null mice had greater lung tissue levels of D(2)- and E(2)-isoprostanes, the precursors of J(2)- and A(2)-isoprostanes, both at base line and following
ozone exposure compared with congenic wild-type mice. We confirmed in primary cultures of normal human bronchial epithelial cells that A(2)-isoprostane inhibited
ozone-induced NF-κB activation and
IL-8 regulation. Furthermore, we determined that A(2)-isoprostane covalently modified the active Cys(179) domain in inhibitory κB
kinase in the presence of
ozone in vitro, thus establishing the biochemical basis for A(2)-isoprostane inhibition of NF-κB. Our results demonstrate that host factors may regulate pulmonary susceptibility to
ozone by regulating the generation of A(2)-isoprostanes in the lung. These observations provide the biochemical basis for the epidemiologic observation that NQO1 regulates pulmonary susceptibility to
ozone.