Application of the EPR spin-trapping technique to the detection of radicals produced in vivo during inhalation exposure of rats to ozone.
Ozone is known to induce lipid peroxidation of lung tissue, although no direct evidence of free radical formation has been reported. We have used the electron paramagnetic resonance (EPR) spin-trapping technique to search for free radicals produced in vivo by ozone exposure. The spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) was administered ip to male Sprague-Dawley rats. The rats were then exposed for 2 hr to either 0, 0.5, 1.0, 1.5, or 2.0 ppm ozone with 8% CO2 to increase their respiratory rate. A six-line 4-POBN/radical spin adduct signal (aN = 15.02 G and a beta H = 3.27 G) was detected by EPR spectroscopy in lipid extracts from lungs of rats treated with 4-POBN and then exposed to ozone. Only a weak signal was observed in the corresponding solution from rats exposed to 0 ppm ozone (air with CO2 only). The concentration of the radical adduct increased as a function of ozone concentration. After administration of 4-POBN, rats were exposed for either 0.5, 1.0, 2.0, or 4.0 hr to either 0 or 2.0 ppm ozone (with CO2). The radical adduct concentration of the ozone-exposed groups at exposure times of 2.0 and 4.0 hr was significantly different from that of the corresponding air control groups. A correlation was observed between the radical adduct concentration and the lung weight/body weight ratio. These results demonstrate that ozone induces the production of free radicals in rat lungs during inhalation exposure and that radical production may be involved in the induction of pulmonary toxicity by ozone. This is the first direct evidence for ozone-induced free radical production in vivo.