Effects of crystalline silica with different exposure patterns on lung fibrosis in rats

Objective: To investigate the effects of crystalline silica with different exposure patterns on lung fibrosis in rats. Methods: A total of 20 adult male Wistar rats were randomly divided into 4 groups consisting of five animals each and received intratracheal instillation of sterile saline or silica suspension in different patterns: saline once at day 0, saline once/week, crystalline silica 50 mg at day 0, crystalline silica 6.25 mg/week. The rats were sacrificed at 8 weeks. The lung tissues were collected for pathological analyses, and determining mRNA and protein levels of related fibrogenic molecules. Results: The collagen deposition induced by crystalline silica in lung tissues were increased. The mRNA levels of IL-1β and Col I in group c were significantly elevated than those in group saline once at day 0 (all P<0.05). Compared with group saline once/week, the mRNA levels of IL-1β, TGF-β, Col I, Col III and CTGF were significantly increased in group crystalline silica 6.25 mg/week (P<0.05) . The mRNA levels of Col I and CTGF were significantly increased in group crystalline silica 6.25 mg/week in comparison with those in group crystalline silica 50 mg at day 0 (P<0.05) . Conclusion: Given the same cumulative dose of crystalline silica, multiple exposures were likely to induce more severe lung fibrosis.