Synergistic toxicological effects of two common ambient air pollutants; ozone and 1-nitronaphthalene

Prof. Alan R. Buckpitt, Dept. of Molecular Biosciences, University of California Davis, USA
Prof. Charles G. Plopper, Dept. of Anatomy, Physiology and Cell Biology, University of California Davis, USA
Prof. Bruce D. Hammock, Department of Entomology and Cancer Research Center, University of California, Davis, USA
Prof. Susumu Goto, Bioinformatics Center, Kyoto University, Japan

Urban air pollution is a growing problem, and many air pollutants have been linked to increased incidence of lung disease. Ozone and 1-nitronaphthalene (1-NN) are common urban air pollutants formed during photochemical smog episodes. Earlier work has shown that the mechanism of 1-NN toxicity is dependant on cytochrome P450-mediated activation in the airway epithelium to form electrophilic metabolites, which then covalently bind to proteins. Previous pathology studies have shown that the toxicity of 1-NN to the airway epithelium is exacerbated in rat by prior long term exposure to ozone. Long-term ozone exposure causes remodeling of the distal airways, rendering the airway resistant to further ozone challenges that normally would cause epithelial necrosis and inflammation in the airway. The observed synergistic toxicity with 1-NN is unexpected given that chronic ozone exposure causes upregulation of both the glutathione pool and glutathione transferase activity, which is the main detoxification pathway for reactive metabolites of 1-NN. Although some increase in P450 dependent 1-NN metabolism has been observed in ozone tolerant animals, the precise mechanism for this synergistic interaction is unknown. In an attempt to elucidate the mechanisms underlying the observed synergistic toxicity, we have investigated the alterations in protein adduct formation and protein expression in subcompartments of the rat respiratory system following ozone and/or 1-NN exposure.

The alterations in protein adduct formation and expression in subcompartments of the lung were analyzed using ultra zoom 2-dimensional electrophoresis (2DE) and mass spectrometry (MS). The first part of these studies was designed to investigate how long-term ozone exposure affects the protein adduction pattern of 1-NN in the airway epithelium. The results demonstrated that several specific proteins, including molecular chaperones and proteins involved in antioxidant defense, are adducted by reactive 1-NN metabolites in vivo [1]. Furthermore, oxidant exposure changes the pattern of adduct formation, and these changes correlated with the increased toxicity observed in previous pathological studies. Prior ozone exposure drastically altered the protein adduction pattern of primarily three of these proteins. Interestingly, these proteins are all multifunctional proteins that besides their well known functions of antioxidant defense and molecular chaperoning have been shown to excerpt immunoregulatory functions. Hypothesizing that adduction of proteins involved in regulation of the inflammatory response be an essential factor in the mechanism underlying the synergistic toxicity of ozone and 1-NN, the examination of a number of inflammatory mediators present in bronchiolar lavage fluid was initiated. Using an LC-MS metabolomics approach, oxylipins and cytokines were analyzed. These studies revealed that prior long-term ozone exposure indeed causes an altered inflammatory response to 1-NN, with a shift to an allergic (Th2) immunological response and altered dose-response of 1-NN [2]. The second, larger part of the study involves examining alterations of the protein expression pattern of the airway epithelium in response to ozone and 1-NN exposure. Both the dose- and time responses of the protein expression are currently being quantified using 2DE analysis, and the proteome is being identified using MALDI ToF-ToF. Read more about the bioinformatics part of this project here.

Last updated: 2008-01-10