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Synergistic Production of Lung Free Radicals by Diesel Exhaust Particles and Endotoxin

Free Radical Metabolite Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina

Correspondence and requests for reprints should be addressed to Ronald P. Mason, Ph.D., Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, National Institutes of Health (NIEHS/NIH), Research Triangle Park, NC 27709. E-mail: mason4{at}niehs.nih.gov

The present study tested the hypothesis that free radicals were involved in the pathogenesis of lung injury caused by diesel exhaust particles (DEP) and bacterial lipopolysaccharides (LPS). Intratracheal coinstillation of DEP and LPS in rat lungs resulted in synergistic enhancement of free radical generation in the lungs. The radical metabolites were characterized as lipid-derived by electron spin resonance (ESR). The free radical generation was paralleled by a synergistic increase in total protein and by infiltration of neutrophils in the bronchoalveolar lavage (BAL) fluid of the lungs. Experiments with NADP-reduced (NADPH) oxidase and iNOS knockout mice showed that NADPH oxidase and iNOS did not contribute to free radical generation. However, pretreatment with the macrophage toxicant GdCl₃, the xanthine oxidase (XO) inhibitor allopurinol, and the Fe^III chelator Desferal resulted in a marked decrease in free radical generation, lung inflammation, and lung injury. These effects were concomitant with the inhibition of XO activity in BAL, suggesting that the activated macrophages and the activity of XO contributed to the generation of free radicals caused by DEP and LPS. This is the first demonstration that DEP and LPS work synergistically to enhance free radical generation in lungs, mediated by the activation of local XO.

Key Words: diesel exhaust particles • ESR spin trapping • free radicals • lipopolysaccharide • xanthine oxidase

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