Cyclic mechanical strain increases reactive oxygen species production in pulmonary epithelial cells

Overdistention of lung tissue during mechanical ventilation may be one of the factors that initiates ventilator-induced lung injury (VILI). We hypothesized that cyclic mechanical stretch (CMS) of the lung epithelium is involved in the early events of VILI through the production of reactive oxygen species ( ROS). Cultures of an immortalized human airway epithelial cell line (16HBE), a human alveolar type II cell line (A549), and primary cultures of rat alveolar type II cells were cyclically stretched, and the production of superoxide (O-2(-)) was measured by dihydroethidium fluorescence. CMS stimulated increased production of O-2(-) after 2 h in each type of cell. 16HBE cells exhibited no significant stimulation of ROS before 2 h of CMS ( 20% strain, 30 cycles/min), and ROS production returned to control levels after 24 h. Oxidation of glutathione (GSH), a cellular antioxidant, increased with CMS as measured by a decrease in the ratio of the reduced GSH level to the oxidized GSH level. Strain levels of 10% did not increase O-2(-) production in 16HBE cells, whereas 15, 20, and 30% significantly increased generation of O-2(-). Rotenone, a mitochondrial complex I inhibitor, partially abrogated the stretch-induced generation of O-2(-) after 2 h CMS in 16HBE cells. NADPH oxidase activity was increased after 2 h of CMS, contributing to the production of O-2(-). Increased ROS production in lung epithelial cells in response to elevated stretch may contribute to the onset of VILI.