Linking oxidative events to inflammatory and adaptive gene expression induced by exposure to an organic particulate matter component

Abstract

Background: Toxicological studies have correlated inflammatory effects of diesel exhaust particles (DEP) with its organic constituents, such as the organic electrophile 1,2-naphthoquinone (1,2-NQ). Objective: To elucidate the mechanisms involved in 1,2-NQ-induced inflammatory responses, we examined the role of oxidant stress in 1,2-NQ-induced expression of inflammatory and adaptive genes in a human airway epithelial cell line. Methods: We measured cytosolic redox status and hydrogen peroxide (H 2O 2) in living cells using the genetically encoded green fluorescent protein (GFP)-based fluorescent indicators roGFP2 and HyPer, respectively. Expression of interleukin-8 (IL-8), cyclooxygenase-2 (COX-2), and heme oxygenase-1 (HO-1) mRNA was measured in BEAS-2B cells exposed to 1,2-NQ for 1-4 hr. Catalase overexpression and metabolic inhibitors were used to determine the role of redox changes and H 2O 2 in 1,2-NQ-induced gene expression. Results: Cells expressing roGFP2 and HyPer showed a rapid loss of redox potential and an increase in H 2O 2 of mitochondrial origin following exposure to 1,2-NQ. Overexpression of catalase diminished the H 2O 2-dependent signal but not the 1,2-NQ-induced loss of reducing potential. Catalase overexpression and inhibitors of mitochondrial respiration diminished elevations in IL-8 and COX-2 induced by exposure to 1,2-NQ, but potentiated HO-1 mRNA levels in BEAS cells. Conclusion: These data show that 1,2-NQ exposure induces mitochondrial production of H 2O 2 that mediates the expression of inflammatory genes, but not the concurrent loss of reducing redox potential in BEAS cells. 1,2-NQ exposure also causes marked expression of HO-1 that appears to be enhanced by suppression of H 2O 2. These findings shed light into the oxidant-dependent events that underlie cellular responses to environmental electrophiles.