Effect of thiol antioxidants on lipopolysaccharide-induced cyclooxygenase-2 expression in pulmonary epithelial cells

Cyclooxygenase-2 (COX-2) plays an important role in pulmonary inflammatory response, and its expression is regulated by several transcription factors including nuclear factor kappa-B (NF-kB), activator protein-1 (AP-1), and signal transducer and activator of transcription-3 (STAT-3), which are activated by oxidative stress. Glutathione (GSH) and N-acetyl cysteine (NAC) are thiol antioxidants that scavenge reactive oxygen species (ROS). The present study investigated whether lipopolysaccharide (LPS) induces COX-2 expression through ROS generation and the activation of oxidant-sensitive transcription factors such as NF-kB, AP-1, and STAT-3 in pulmonary epithelial A549 cells. The cells were pretreated with GSH or NAC for 1 hour prior to LPS stimulation. Intracellular ROS levels, DNA-binding activities of NF-kB, AP-1, and STAT-3, and mRNA and protein levels of COX-2 were determined. Our results showed that LPS increased ROS levels that peaked at 2 hours. LPS activated NF-kB, AP-1, and STAT-3 and induced the expression of COX-2 in A549 cells in a timedependent manner. Pretreatment of thiol antioxidants GSH and NAC reduced ROS levels and attenuated the increase in ROS, the activation of NF-kB, AP-1, and STAT-3, and the expression of COX-2 in LPS-treated A549 cells. In conclusion, GSH and NAC suppress COX-2 expression by reducing ROS levels and inhibiting the activation of NF-kB, AP-1, and STAT-3 in pulmonary epithelial A549 cells exposed to LPS. Pretreatment with thiol antioxidants GSH and NAC may be beneficial for the treatment of pulmonary inflammation associated with oxidative stress.