Hyperoxia alters the mechanical properties of alveolar epithelial cells

Abstract

Patients with severe acute lung injury are frequently administered high concentrations of oxygen (Ͼ50%) during mechanical ventilation. Long-term exposure to high levels of oxygen can cause lung injury in the absence of mechanical ventilation, but the combination of the two accelerates and increases injury. Hyperoxia causes injury to cells through the generation of excessive reactive oxygen species. However, the precise mechanisms that lead to epithelial injury and the reasons for increased injury caused by mechanical ventilation are not well understood. We hypothesized that alveolar epithelial cells (AECs) may be more susceptible to injury caused by mechanical ventilation if hyperoxia alters the mechanical properties of the cells causing them to resist deformation. To test this hypothesis, we used atomic force microscopy in the indentation mode to measure the mechanical properties of cultured AECs. Exposure of AECs to hyperoxia for 24 to 48 h caused a significant increase in the elastic modulus (a measure of resistance to deformation) of both primary rat type II AECs and a cell line of mouse AECs (MLE-12). Hyperoxia also caused remodeling of both actin and microtubules. The increase in elastic modulus was blocked by treatment with cytochalasin D. Using finite element analysis, we showed that the increase in elastic modulus can lead to increased stress near the cell perimeter in the presence of stretch. We then demonstrated that cyclic stretch of hyperoxia-treated cells caused significant cell detachment. Our results suggest that exposure to hyperoxia causes structural remodeling of AECs that leads to decreased cell deformability.acute respiratory distress syndrome; atomic force microscopy; force maps; elastic modulus THE MORTALITY RATE OF 40 -60% for patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) remains remarkably high in the United States (36). Patients with ALI and ARDS exhibit compromised respiratory function that is partly related to edema formation attributable to loss of endothelial and epithelial barrier integrity (26,40,42). Fluid accumulation in the alveolar space ultimately diminishes the efficiency of gas exchange, causing hypoxemia. Although patients are often initially treated with oxygen by mask, the extent of injury frequently requires mechanical ventilation with supplemental oxygen. Although mechanical ventilation is necessary for the survival of patients with the most severe physiological impairment, additional injury can occur, and this is referred to as ventilator-induced lung injury (12,23,33). Both mechanical ventilation and long-term exposure to hyperoxia can independently cause lung injury that is similar histologically to that seen in ARDS (1, 10, 24). Furthermore, animal studies have shown that the use of high levels of inspired oxygen (FI O 2 Ͼ50%) can accelerate and increase lung injury when used in conjunction with high-stretch mechanical ventilation (2,10,17,19,20,31). However, the mechanisms responsible for this enhanced injury are not well unde...

Should Oxygen Therapy Be Tightly Regulated to Minimize Hyperoxia in Critically Ill Patients?

“…24,[26][27][28][29][30][31][32][33][34][35][36] These models mimic common clinical strategies in managing ARDS and other forms of acute respiratory failure before the advent of lung-protective ventilation. In brief, compared with controls, high-V T ventilation with ambient F IO 2 (0.21), or a physiologic V T with hyperoxia, the combination of high-V T (18 -30 mL/kg) ventilation, and hyperoxia (F IO 2 ϭ 0.8 -1.0) markedly enhanced numerous signifiers for VILI, including: altered-permeability pulmonary edema formation, 24,26,27,31,32 diffuse interstitial and alveolar hemorrhage, 33,34 decreased surfactant production (Fig.…”

Coming to terms with tissue engineering and regenerative medicine in the lung

“…and other important lung ECM components. Indeed, there is now increasing evidence that mechanical forces per se can, on the one hand, influence ECM composition (200), whereas on the other, the ECM influences the cellular properties in the lung (33,88,134,164,173,195). Mechanical properties and forces can further modulate cell fate, particularly the differentiation of stem cells on the basis of mechanotransduction (48,49,149,161,204).…”

“…For example, even brief periods of alveolar stretch can induce an inflammatory cascade (227) that can in turn influence alveoli and the pulmonary vasculature. Here, the extent of stretch is likely important (8,40,163,195), and stretch effects may involve a range of pathways including Fas/FasL (93), Rac1 (41), PLA2 (116), GEF-H1 (17), caveolins (222), and Rho kinase (42), with modulating effects of oxygen (78,164), ROS (31), and inflammation per se (72,82).…”

Live Cell Imaging during Mechanical Stretch

“…Several studies suggest that excessive mechanical stretch of lung epithelial cells can cause direct injury involving damage to cells 11,13,26,27 . This type of damage is difficult to capture without real-time imaging during the mechanical distention.…”

“…In the respiratory system, one outcome of mechanotransduction is the increase in reactive oxygen species (ROS) 8,9 and pro-inflammatory cytokines 10 in pulmonary epithelial cells in the presence of cyclic tensile strain. Strong evidence also suggests that excessive tensile strain leads to direct injury to the alveolar epithelium, in addition to the biochemical responses of cells [11][12][13][14] . Although the focus here is primarily on the response of lung cells to mechanical deformation, pathways induced by mechanotransduction play a key role in the basic function of many tissues in the human body, including the regulation of vascular tone 15 and the development of the growth plate 16 .…”