Effects of Acute Inhalation of Respirable Coal Fly Ash on Metabolic Defense Capability of the Rat Lung

Abstract

Effects of acute, 4-wk inhalation of respirable coal fly ash aerosol on the pulmonary metabolic defense capability were studied in rats. The fly ash was collected from the baghouse of a small, underfeeder-type coal combustor used for greenhouse heating. Effects were studied by measuring alterations in activities of specific antioxidant and drug metabolizing enzymes in rat lungs. Fly ash exposure for 6 hlday and 5 dayslwk during 4 wk to 10, 30, or 700 mg/m³ significantly increased the cytosolic protein level and the activities of glutathione peroxidase and glucose-6-phosphate dehydrogenase. Fly ash also enhanced the microsomal protein level, although the total cytochrome P-450 content was not changed. Fly ash caused a dual effect on cytochrome P-450 isoenzyme-related substrate metabolism. The O-deethylation of ethoxyresorufin was increased, whereas O-dearylation of benzoxyresorufin was decreased. The above results indicate that subacute inhalation of respirable coal fly ash aerosol in rats is able to increase as well as decrease distinct components of the metabolic defense capability of lungs. The data were compared with those resulting from exposure to ozone, a well-known air pollution oxidant, at a level that caused severe toxic effects in the lungs, and with those resulting from two enzyme induction studies using the model inducers phenobarbitone and O-naphthoflavone. The results suggest that poly-cyclic aromatic hydrocarbons and toxic trace elements of the fly ash are responsible for these dual effects on lung cytochrome P-450 enzymes, that is, induction and inhibition of these activities, respectively.