Ja. Dye et al., Ozone effects on airway responsiveness, lung injury, and inflammation. Comparative rat strain and in vivo/in vitro investigations, INHAL TOXIC, 11(11), 1999, pp. 1015-1040
Asthmatic individuals appear to be particularly sensitive to the effects of
certain air pollutants-including ozone (O-3), an oxidant ambient air pollu
tant-for reasons that are poorly understood. The general purpose of these s
tudies, therefore, was to expand and improve upon toxicologic methods for a
ssessing ozone-induced effects on the airways of the rat by (1) developing
an in vivo testing procedure that allows detection of airway responsiveness
changes in rats exposed to ozone; (2) identifying a strain of rat that may
be inherently more sensitive to the effects of ozone; and (3) validation o
f an in vitro epithelial culture system to more directly assess airway cell
ular/subcellular effects of ozone. Using methacholine inhalation challenges
, we detected increased airway responsiveness in senescent F344 rats acutel
y after ozone exposure (2 ppm x 2 h). We also determined that acutely after
ozone exposure (0.5 ppm x 8 h), Wistar rats developed significantly greate
r lung injury, neutrophilic inflammation, and bronchoalveolar lavage (BAL)
fluid concentrations of IL-6 than either Sprague-Dawley (SD) or F344 rats.
SD rats had greater BAL fluid concentrations of prostaglandin E-2 (PGE(2)),
while F344 rats consistently exhibited the least effect. Wistar rat-derive
d tracheal epithelial (RTE) cultures were exposed in vitro to air or ozone
(0.1-1.0 ppm x 1 h), and examined for analogous effects. in a concentration
-dependent manner, ozone exposure resulted in acute but minor cytotoxicity.
RT polymerase chain reaction (PCR) analysis of RNA isolated from ozone-exp
osed cells demonstrated variable increases in steady-state gene expression
of IL-6 at 4 h postexposure, while at 24 h cellular fibronectin expression
(EIIIA domain) was decreased. Exposure was without effect on macrophage inf
lammatory protein 2 (MIP-2) or gamma-glutamyl cysteine synthetase expressio
n. At 6 h postexposure, IL-6 synthesis and apical release appeared increase
d in ozone-exposed cells (1 ppm x 1 h). MIP-2 release was not significantly
increased in ozone-exposed cells. Al 2 h postexposure, ozone exposure resu
lted in minor increases in apical fibronectin, but exposure was without eff
ect on basolateral accumulation of fibronectin. Exposure to 1.0, but nor 0.
1 ppm (x 1 h), increased production of cyclooxygenase (i.e., PGE(2)) and no
ncyclooxygenase products of arachidonic acid. Results demonstrate that mult
iple inflammatory mediator pathways are affected by ozone exposure. Such ef
fects could exacerbate morbidity in individuals with preexisting airway inf
lammation such as asthmatics.