Silica earth provoked lung fibrosis with stimulation of lysosomal enzymes and lipid peroxidation in rats.

The dynamics of the biological response of pulmonary tissue to silica dust (silica earth from Piotrowice, Poland, recommended as a domestic reference fibrogenic standard) was studied in rats after single-shot intratracheal instillation of a suspension of 20 mg of the dust for one, three, and seven months. Silica dust provoked pronounced pulmonary fibrosis as inferred from increased collagen content together with pathomorphological alteration (silicotic nodules). The lung burden of silica dust affected the lysosomal subfraction as manifested by an increase in its protein content with concomitant stimulation (release and presumably induction) of beta-glucuronidase and cathepsin D and a transient (up to three months) stimulation of lipid peroxidation. Stimulation of activity of lysosomal enzymes and lipid peroxidation mediated by silica dust may reflect destructive metabolic processes resulting in the development of pulmonary fibrosis as the sign of a pathological repair mechanism. The extent of the effects brought about by silica earth testify that it may be recommended as a reference standard for evaluating the potential health hazard from industrial exposure to dusts containing SiO2.