Changes in Alveolar Lavage Materials and Lung Microsomal Xenobiotic Metabolism Following Exposures to HCl-Washed or Unwashed Crystalline Silica

Intratracheal exposures of rats to crystalline silica washed with HCl to remove iron contaminants have previously been shown to increase lung surfactant phospholipids (PL) and proteins and to alter the pulmonary microsomal cytochrome P450 system. We compared these effects of HCl-washed silica with those produced by exposures to unwashed silica and alumina. Both silica preparations produce increases in lung weights and alveolar lavage PL and proteins, but to different degrees. The increases produced by HCl-washed vs unwashed silica are lung weights, 2.2- vs 1.3-fold; lavage FL, 25.9- vs 3.7-fold; and lavage proteins, 11.1- vs 3.2-fold, respectively. Although the two silica particles increase lung microsomal protein concentrations (expressed per gram lung) by 50-60%, their effects on cytochrome P-450-mediated xenobiotic metabolism are quite different. Exposure to HCl-washed silica leads to a 2.3-fold increase in 7-ethoxyresorufin O-deethylation, a reaction catalyzed by cytochrome P4501A1, and a 0.5- to 0.6-fold reduction in 7-ethoxycoumarin O-deethylation, a reaction which may be catalyzed by cytochrome P-4502B1. Unwashed silica does not alter the metabolism of either xenobiotic when results are expressed per milligram microsomal protein. Administration of alumina produces only minor increases in lung weight and lavage PL and no effect on microsomal xenobiotic metabolism. These results show that the increases in alveolar lavage PL and proteins induced by administration of unwashed silica are exaggerated by 3- to 7-fold if the silica is treated with HCl. Furthermore, exposure to HCl-washed silica results in significant alterations of the lung microsomal cytochrome P450 system, but the unwashed silica has little effect. Although the reason(s) for these different effects is not known, measurements of iron levels and formation of hydroxyl radicals using ESR demonstrate that there is more iron associated with the unwashed than with the HCl-washed silica.