Lipopolysaccharide induces apoptotic insults to human alveolar epithelial A549 cells through reactive oxygen species-mediated activation of an intrinsic mitochondrion-dependent pathway.
Alveolar type II epithelial cells can regulate immune responses to sepsis-induced acute lung injury. Lipopolysaccharide (LPS), an outer membrane component of Gram-negative bacteria, can cause septic shock. This study was designed to evaluate the cytotoxic effects of LPS on human alveolar epithelial A549 cells and its possible molecular mechanisms. Exposure of A549 cells to LPS decreased cell viability in concentration- and time-dependent manners. In parallel, LPS concentration- and time-dependently induced apoptosis of A549 cells. Meanwhile, LPS only at a high concentration of 10 μg/ml caused mildly necrotic insults to A549 cells. In terms of the mechanism, exposure of A549 cells to LPS increased the levels of cellular nitric oxide and reactive oxygen species (ROS). Pretreatment with N-acetylcysteine (NAC), an antioxidant, significantly lowered LPS-caused enhancement of intracellular ROS in A549 cells and simultaneously attenuated the apoptotic insults. Sequentially, treatment of A549 cells with LPS caused significant decreases in the mitochondrial membrane potential and biosynthesis of adenosine triphosphate. In succession, LPS triggered the release of cytochrome c from the mitochondria to the cytoplasm. Activities of caspase-9 and caspase-6 were subsequently augmented following LPS administration. Consequently, exposure of A549 cells induced DNA fragmentation in a time-dependent manner. Pretreatment of A549 cells with NAC significantly ameliorated LPS-caused alterations in caspase-9 activation and DNA damage. Therefore, this study shows that LPS specifically induces apoptotic insults to human alveolar epithelial cells through ROS-mediated activation of the intrinsic mitochondrion-cytochrome c-caspase protease mechanism.
Chuang
Chi-Yuan
CY
Graduate Institute of Clinical Medicine, Taipei Medical University, Taiwan.
Chen
Ta-Liang
TL
Cherng
Yih-Giun
YG
Tai
Yu-Tyng
YT
Chen
Tyng-Guey
TG
Chen
Ruei-Ming
RM
D000111:Acetylcysteine / Q000378:metabolism; D056809:Alveolar Epithelial Cells / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D053178:Caspase 6 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D053938:DNA Fragmentation; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000187:drug effects; D006801:Humans; D008070:Lipopolysaccharides / Q000493:pharmacokinetics*; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism* / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013997:Time Factors
D008070:Lipopolysaccharides; D017382:Reactive Oxygen Species; D009569:Nitric Oxide; D045304:Cytochromes c; D053178:Caspase 6; D053453:Caspase 9; D000111:Acetylcysteine