Interfacial phospholipids inhibit ozone-reactive absorption-mediated cytotoxicity in vitro

The intrapulmonary distribution of inhaled ozone (O(3)) and induction of site-specific cell injury are related to complex interactions among airflow patterns, local gas-phase concentrations, and the rates of O(3) flux into, and reaction and diffusion within, the epithelial lining fluid (ELF). Recent studies demonstrated that interfacial phospholipid films appreciably inhibited NO(2) absorption. Because surface-active phospholipids are present on alveolar and airway interfaces, we investigated the effects of interfacial films on O(3)-reactive absorption and acute cell injury. Compressed films of dipalmitoyl-glycero-3-phosphocholine (DPPC) and rat lung lavage lipids significantly reduced O(3)-reactive absorption by ascorbic acid, reduced glutathione, and uric acid. Conversely, unsaturated phosphatidylcholine films did not inhibit O(3) absorption. We evaluated O(3)-mediated cell injury using a human lung fibroblast cell culture system, an intermittent tilting exposure regimen to produce a thin covering layer, and nuclear fluorochrome permeability. Exposure produced negligible injury in cells covered with MEM. However, addition of AH(2) produced appreciable (<50%) cell injury. Film spreading of DPPC monolayers necessitated the use of untilted regimens. Induction of acute cell injury in untilted cultures required both AH(2) plus very high O(3) concentrations. Addition of DPPC films significantly reduced cell injury. We conclude that acute cell injury likely results from O(3) reaction with ELF substrates. Furthermore, interfacial films of surface-active, saturated phospholipids reduce the local dose of O(3)-derived reaction products. Finally, because O(3) local dose and tissue damage likely correlate, we propose that interfacial phospholipids may modulate intrapulmonary distribution of inhaled O(3) and the extent of site-specific cell injury.