Icaritin attenuates cigarette smoke-mediated oxidative stress in human lung epithelial cells via activation of PI3K-AKT and Nrf2 signaling

Icariin is the major active ingredient of Herba Epimedii. Icaritin (ICT) is a hydrolytic product of Icariin. In the present study, we investigated the protective role of ICT against cigarette smoke extract (CSE)-mediated oxidative stress in human lung epithelial A549 cells. As demonstrated by the WST-8 assay, exposure to CSE (2.5%, 5%, and 10%) reduced the cell viability of A549 cells (84%, 64% and 53%) in a dose-dependent manner and treatment with ICT 10 μM dramatically attenuated CSE induced cytotoxicity (73% and 64%). The MFI data suggested that CSE induced oxidative stress by generating ROS (230) and 10 μM ICT treatment attenuated CSE-induced ROS production (90). 10 μM ICT treatment resulted in significant AKT activation, Nrf2 nuclear translocation, increased GCL transcription and GSH levels, as compared with CSE exposure alone. However, ICT-mediated upregulation of GCL transcription in CSE-treated cells were lost in Nrf2 siRNA-transfected cells. Furthermore, inhibition of PI3K/AKT signaling by LY294002 partially prevents ICT-induced nuclear translocation of Nrf2 and GCL transcription. These findings suggest that ICT attenuates CS-induced oxidative stress by quenching ROS and also by upregulating GSH via a PI3K-AKT-Nrf2-dependent mechanism. Further studies are required to confirm that a similar protective effect of ICT occurs in the lungs in vivo in response to CS exposure.