Comparative in vitro studies on the fibrogenic effects of two samples of silica on epithelial bronchial cells

The small dimension and particle shape of silica in gypsum used to prepare moulds for lost wax casting might be responsible for the high prevalence of silicosis in gold jewellery. To test this hypothesis, human pulmonary epithelial cell (BEAS-2B) cultures were exposed to two samples of silica with different crystal micro-morphologies: Silica Powder (Silica P) which is used in casting gold jewellery, and no powder Silica (Silica F). Extracellular matrix (ECM) production was evaluated using radio-labelled precursors and quantified by RT-PCR analysis. Expression of basic fibroblast growth factor (FGF2) and its receptor (FGFR2) was also evaluated. The results demonstrated Silica P particles had a very fine lamellar crystalline structure while Silica F was characterized by larger rounded crystals. Silica P stimulated collagen production significantly more than Silica F and downregulated laminin and metalloprotease expression. Both silica samples down-regulated FGF2 but only Silica F enhanced FGF2 receptor expression. In conclusion each Silica sample promoted a profibrotic lung microenvironment in a different manner and also elicited different FGF2 signalling pathways. The data confirm that different micromorphology of Silica particles affects the fibrogenic potential and the molecular mechanisms of dust pathogenicity.