Ginkgo biloba extract confers protection from cigarette smoke extract-induced apoptosis in human lung endothelial cells: Role of heme oxygenase-1

Cigarette smoking is the major cause of chronic obstructive pulmonary disease, which is associated with increased oxidative stress and numbers of apoptotic endothelial cells in the lungs. Ginkgo biloba extract (EGb) is a therapeutic agent for disorders such as vascular insufficiency and Alzheimer's disease. Although EGb is known to possess antioxidant functions, its ability to alleviate cigarette smoke-induced pathophysiological consequences has not been elucidated. We investigated the cytoprotective effects and therapeutic mechanisms of EGb against oxidative stress and apoptosis induced by cigarette smoke extract (CSE) in human pulmonary artery endothelial cells (HPAECs). Challenge with CSE (160 μg/ml) caused a reduction in cell viability, an increase in intracellular reactive oxygen species and an acceleration of caspase-dependant apoptosis in HPAECs, all of which were alleviated by pretreatment with EGb (100 μg/ml). N-acetylcysteine (an antioxidant) also reduced both the CSE-induced oxidative stress and apoptosis, indicating that the former response trigged the latter. Additionally, EGb produced activation of ERK, JNK and p38 [three major mitogen-activated protein kinases (MAPKs)], an increase in the nuclear level of nuclear factor erythroid-2-related factor 2 (Nrf2) and upregulation of heme oxygenase-1 (HO-1, a stress-responsive protein with antioxidant function). Pretreatment with inhibitors of MAPKs abolished both EGb-induced Nrf2 nuclear translocation and HO-1 upregulation. Small interfering RNAs targeting HO-1 prevented EGb-induced HO-1 upregulation and also abolished the antioxidant, anti-apoptotic and cytoprotective effects of EGb in HPAECs insulted with CSE. We conclude that EGb confers protection from oxidative stress-related apoptosis induced by CSE in HPAECs and its therapeutic effects depend on transcriptional upregulation of HO-1 by EGb via the MAPKs/Nrf2 pathway.