Airborne Particulate Matter (PM) Inhibits Apoptosis through PI3K/AKT/FoxO3a Pathway in Lung Epithelial Cells: The Role of a Second Oxidant Stimulus.

Outdoor particulate matter (PM) exposure is carcinogenic to humans. The cellular mechanism by which PM is associated specifically with lung cancer includes oxidative stress and damage to proteins, lipids, and DNA in the absence of apoptosis, suggesting that PM induces cellular survival. We aimed to evaluate the PI3K/AKT/FoxO3a pathway as a mechanism of cell survival in lung epithelial A549 cells exposed to PM that were subsequently challenged with hydrogen peroxide (HO). Our results showed that pre-exposure to PM followed by HO, as a second oxidant stimulus increased the phosphorylation rate of pAKT, pAKT, and pFoxO3a 2.5-fold, 1.8-fold, and 1.2-fold, respectively. Levels of catalase and p27, which are targets of the PIK3/AKT/FoxO3a pathway, decreased 38.1% and 62.7%, respectively. None of these changes had an influence on apoptosis; however, the inhibition of PI3K using the LY294002 compound revealed that the PI3K/AKT/FoxO3a pathway was involved in apoptosis evasion. We conclude that nontoxic PM exposure predisposes lung epithelial cell cultures to evade apoptosis through the PI3K/AKT/FoxO3a pathway when cells are treated with a second oxidant stimulus.