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 NO2 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.