Paraquat-Induced Reactive Oxygen Species Inhibit Neutrophil Apoptosis via a p38 MAPK/NF-κB-IL-6/TNF-α Positive-Feedback Circuit

Paraquat (PQ), a widely used herbicide and potent reactive oxygen species (ROS) inducer, can injure multiple tissues and organs, especially the lung. However, the underlying mechanism is still poorly understood. According to previous reports, neutrophil aggregation and excessive ROS production might play pivotal pathogenetic roles. In the present study, we found that PQ could prolong neutrophil lifespan and induce ROS generation in a concentration-independent manner. Activated nuclear factor-kappa B (NF-kappa B), p38 mitogen-activated kinase (p38 MAPK), and myeloid cell leukemia sequence 1 (Mcl-1) but not Akt signaling pathways were involved in this process, as well as increasing levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and IL-1 beta. Furthermore, the proinflammatory mediators IL-6 and TNF-alpha could in turn promote ROS generation, creating a vicious cycle. The existence of such a feedback loop is supported by our finding that neutrophil apoptosis is attenuated by PQ in a concentration-independent manner and could partially explain the clinical dilemma why oxygen therapy will exacerbate PQ induced tissue injury.