Silica-induced generation of reactive oxygen species in Rat2 fibroblast: Role in activation of mitogen-activated protein kinase

Exposure to silica has been associated with progressive pulmonary inflammation and fibrosis. While the fibroblasts play an important role in the pathogenesis of silicosis, the direct interaction between silica and fibroblasts is poorly understood. We observed that silica particles stimulated intracellular ROS generation in Rata fibroblast, evidenced by DCFH oxidation, Silica-induced DCFH oxidation was inhibited by catalase and DPI, a flavoenzyme inhibitor. Additionally, the time course of elevation of the intracellular ROS was paralleled by the increases of MEK and ERK phosphorylation, Silica-induced ERK phosphorylation was also effectively attenuated by catalase and DPI. However, SOD enhanced the silica-induced ERK phosphorylation, indicating a role for H2O2 in ERK activation. Furthermore, ERK and MEK phosphorylation are reproduced by H2O2 treatment. Taken together, these results demonstrate that silica stimulates ROS production via flavoenzyme-dependent mechanism in Rata fibroblasts and the H2O2, in turn, serves as a signal transduction element in activating MEK-ERK pathway. (C) 1999 Academic Press.