Real Time Adaptations of Human Airway Epithelial Cells Exposed to the Environmental Peroxide Isoprene Hydroxy Hydroperoxide
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Exposure to a variety of air pollutants, including ozone, particulate matter, and secondary organic aerosols (SOA), results in the generation of reactive oxygen species (ROS) and the induction of oxidative stress, however, the underlying mechanism(s) remain poorly understood. Within cells, ROS regulate critical signaling pathways, although supra-physiological levels of ROS disrupt intracellular redox homeostasis resulting in the inappropriate oxidation of regulatory thiols. Intracellular redox homeostasis is maintained by a high ratio of reduced to oxidized glutathione (GSH and GSSG, respectively), which is sustained at the expense of NADPH. In the current study, we investigated the effect of isoprene hydroxy hydroperoxide (ISOPOOH), an environmental peroxide and known constituent of SOA, on a variety of redox endpoints. Our approach relies on high resolution live cell imaging of human airway epithelial cells (HAECs), expressing genetically encoded ratiometric biosensors GRX1-roGFP2, iNAP1, or HyPER, to monitor changes in the glutathione redox potential (EGSH), NADPH, and H2O2, respectively. Non-cytotoxic exposure of HAECs to ISOPOOH resulted in transient increases in EGSH, which were markedly enhanced following glucose deprivation, concomitant with lowered NADPH levels. Addition of 1 mM glucose rapidly restored EGSH and NADPH levels, while 30 uM glucose induced bi-modal recovery. Alternatively, the introduction of 2-deoxyglucose (2-DG) differentially impacted recovery of EGSH and NADPH levels. To modulate glucose-mediated recovery of EGSH and NADPH levels, we investigated the role of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme in the pentose phosphate pathway. Complete knockout of G6PD markedly impaired glucose-mediated recovery of EGSH but not NADPH levels. These findings highlight adaptive mechanisms involved in the cellular response to ISOPOOH, while providing insight into the dynamic regulation of intracellular redox homeostasis in the human airway. This abstract of a proposed presentation does not necessarily reflect EPA policy.