# Effects of Oxidized Pyrenes on the Biological Responses in the Human Bronchial Epithelial Cells
## 4 Discussion  
Several in vivo studies have shown that intratracheal exposure to PM induces airway inflammation [14; 15; 16]. Previous in vivo studies, including those by our group, have demonstrated that diesel exhaust particles (DEPs) can affect the respiratory system by inducing edematous changes [17], carcinogenesis [18], airway inflammation with hyperresponsiveness [19], enhancement of allergic lung inflammation [20; 21], and neutroph lung inflammation [22]. However, the exact components of PM/DEP that cause these issues remain unknown. Environmental quinones have toxic effects on living organisms. The toxic effects of DEPs are attributed to PAH quinones [23; 24]. These have been found in ambient PM [25; 26], automotive exhaust emissions [27], and wood smoke particles [28]. Quinones can cause nephrotoxicity, neurotoxicity, and carcinogenesis [29], along with mitochondrial dysfunction [30]. Moreover, certain quinones can generate ROS, including superoxides, hydrogen peroxide, and hydroxyl radicals, which result in cellular damage [31]. Phenanthraquinone is a quinone found at significant concentrations in DEPs [26; 32]. We have previously shown that a single intratracheal instillation of phenanthraquinone in mice can induce the recruitment of inflammatory cells, such as neutrophils and eosinophils, to the airway [10]. Additionally, naphthoquinone, another quinone, can exacerbate allergic lung inflammation [12; 13]. In this study, 1 uM of 4,5-PyQ or 1 and 3 uM of a mixture of 1,8-PyQ + 1,6-PyQ were found to significantly induce epithelial cell activation. Combined with previous findings, the results of this study indicate that quinones might contribute to PM-mediated respiratory toxicity, thereby resulting in airway pathophysiology. Future in vivo studies are required to further understand their role, including studies determining the harmful effects of these quinones on airway diseases such as asthma, pneumonia, and chronic obstructive pulmonary disease (COPD). ICAM-1 (CD54) is an adhesion molecule belonging to the immunoglobulin superfamily, and it is essential for the accumulation of inflammatory cells including neutrophils, eosinophils, and T lymphocytes. [PERSON] et al. [14] demonstrated that neutrophil adhesion to the epithelial cell layer is regulated by ICAM-1 because this adhesion is abrogated after treatment with an anti-ICAM-1 antibody. Moreover, anti-ICAM-1 antibodies significantly blocked inflammatory responses in animal models of asthma [33]. Increased levels of serum and/or bronchoalveolar lavage fluid sICAM-1 have been reported in several inflammatory lung disorders such as sarcoidosis and bronchial asthma [34; 35]. Hence, ICAM-1 expression might be responsible for regulating local inflammatory responses in the lungs. Consistent with this, the DEP-induced upregulation of ICAM-1 in the epithelium may increase neutrophil attachment in vitro [36]. We have previously shown that DEP facilitates the local ICAM-1 expression in a murine model of acute respiratory distress syndrome, which is concomitant with neutroph lung inflammation and enhanced expression of keratinocyte-derived chemokines in the lung in vivo [22]. Therefore, the DEP-induced upregulation of ICAM-1 may be related to its adjuvant, as previously shown in animals [20]. Direct exposure to DEP is reported to induce the upregulation of cell adhesion molecules in endothelial cells [37]. In this study, we observed that at 10 uM, 1,8-PyQ + 1,6-PyQ induced significantly higher levels of sICAM-1 than those in the control, implying that these quinones might cause PM-induced pulmonary toxicity concomitant with ICAM-1 activation. Nevertheless, the conflicting relationship between inflammatory cytokines and sICAM-1 following 1,8-PyQ + 1,6-PyQ exposure at this concentration remains unclear and warrants further experiments. We observed that exposure to more than 3 uM of 4,5-PyQ or 10 uM of 1,8-PyQ + 1,6-PyQ induced cell death, but its pattern was different in cells treated with both quinones because 4,5-PyQ possibly induced cellular apoptosis.