Early Mechanistic Events Induced by Low Molecular Weight Polycyclic Aromatic Hydrocarbons in Mouse Lung Epithelial Cells: A Role for Eicosanoid Signaling

Low molecular weight polycyclic aromatic hydrocarbons (LMW PAHs;< 206.3 g/mol) are under regulated environmental contaminants (eg, secondhand smoke) that lead to gap junction dysregulation, p38 MAPK activation, and increased mRNA production of inflammatory mediators, such as cytokines and cyclooxygenase (COX2), in lung epithelial cells. However, the early mechanisms involving lipid signaling through the arachidonic acid pathway and subsequent eicosanoid production leading to these downstream events are not known. Common human exposures are to mixtures of LMW PAHs, thus C10 cells (a mouse lung epithelial cell line) were exposed to a representative binary PAH mixture, 1-methylanthracene (1-MeA) and fluoranthene (Flthn), for 30 min-24h with and without p38 and cytosolic phospholipase A(2) (cPLA(2)) inhibitors. Cytosolic phospholipase A(2) inhibition reversed PAH-induced phospho-p38 MAPK activation and gap junction dysregulation at 30 min. A significant biphasic increase in cPLA(2) protein was observed at 30 min, 2, and 4h, as well as COX2 protein at 2 and 8h. Untargeted metabolomics demonstrated a similar trend with significantly changing metabolites at 30 min and 4 h of exposure relative to 1h; a cPLA(2)-like subset of metabolites within the biphasic response were predominately phospholipids. Targeted metabolomics showed several eicosanoids (eg, prostaglandin D-2 (PGD(2)), PGE(2 alpha)) were significantly increased at 4, 8, and 12h following exposure to the binary PAH mixture and this effect was p38-dependent. Finally, PAH metabolism was not observed until after 8h. These results indicate an early lipid signaling mechanism of LMW PAH toxicity in lung epithelial cells due to parent PAH compounds.