| Abstrakt: |
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 O3comes into contact and thus represent a potential major target of acute O3toxicity. 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 O3in vitroand monitored effects of O3exposure on activation of phospholipases A2(PLA2), C (PLC), and D (PLD), as well as release of the humoral mediator, platelet activating factor (PAF). PLA2acts 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 PLA2inhibitor mepacrine (1 mM), suggesting a connection between PAF release and PLA2activation. O3exposure 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 O3for 1 hr (417 ± 121% of air control, n= 6). PAF receptor antagonists Ro 24-4736 (1 μM) and Ro 41-5036 (1 μM) did not affect O3-stimulated inositol phosphate accumulation. PLD also was activated in GPTE cells exposed to 1.0 ppm O3for 1 hr (169 ± 80% of air control, n= 5). These results suggest that GPTE cells respond to O3exposure in vitroby 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. |
