Ozone stimulates release of platelet activating factor and activates phospholipases in guinea pig tracheal epithelial cells in primary culture.

Inhalation of ozone (O3) has been associated with development of inflammation in the respiratory airways and a variety of alterations in pulmonary function. Epithelial cells lining the airways are the first cells with which inhaled O3 comes into contact and thus represent a potential major target of acute O3 toxicity. In addition, upon appropriate stimulation or injury, these cells are capable of releasing a spectrum of secondary mediators that could relate to the pathogenesis of O3-associated lesions. We exposed organotypically cultured guinea pig primary tracheal epithelial (GPTE) cells in an air/liquid interface to photochemically generated O3 in vitro and monitored effects of O3 exposure on activation of phospholipases A2 (PLA2), C (PLC), and D (PLD), as well as release of the humoral mediator, platelet activating factor (PAF). PLA2 acts on ether-linked phosphatidylcholine, which upon further metabolism forms PAF;PLC acts on inositol phospholipids to produce inositol phosphates and diacylglycerol; and PLD generates phosphatidic acid. GPTE cell cultures exposed to O3 (0.05-1.0 ppm) for 1 hr displayed an elevated total release of PAF (apical+basolateral). Maximal stimulation in both apical and total release of PAF occurred at 1.0 ppm O3 (405 +/- 47 and 282 +/- 23% of air control values, respectively, n = 7). The 1.0 ppm O3-induced increased PAF release was significantly inhibitable by the PLA2 inhibitor mepacrine (1 mM), suggesting a connection between PAF release and PLA2 activation. O3 exposure activated PLC in GPTE cells in a concentration- (0.1-1.0 ppm) and time-dependent (10-60 min) manner to produce a significant accumulation of inositol-1,4,5-triphosphate, with maximal accumulation at 1.0 ppm O3 for 1 hr (417 +/- 121% of air control, n = 6). PAF receptor antagonists Ro 24-4736 (1 microM) and Ro 41-5036 (1 microM) did not affect O3-stimulated inositol phosphate accumulation. PLD also was activated in GPTE cells exposed to 1.0 ppm O3 for 1 hr (169 +/- 80% of air control, n = 5). These results suggest that GPTE cells respond to O3 exposure in vitro by increasing production and/or release of PAF via a mechanism that may involve activation of PLA2, PLC, and PLD. Epithelial-derived mediators, such as PAF, may play a role in the pathogenesis of lesions associated with inhalation of O3.