Dependence of NF-kappa B activation and free radical generation on silica-induced TNF-alpha production in macrophages

Tumor necrosis factor alpha (TNF alpha) plays an important role in the path ogenesis of silicosis and other chronic inflammatory lung diseases. The pre sent study investigates the role nuclear transcription factor kappa B (NF-k appa B) and oxygen free radicals in silica-induced TNF alpha production in primary alveolar macrophages and RAW 264.7 cells. Using electrophoretic mob ility shift assay (EMSA) and enzyme-linked immunoadsorbent assay (ELISA), w e have demonstrated that silica can induce NF-kappa B activation and TNF al pha expression in a dose-dependent manner. Transient transfection assays wi th a plasmid construct containing NF-kappa B binding sites linked to a repo rter gene further show that silica is able to induce the transcriptional ac tivation of NF-kappa B-dependent gene. Inhibition of NF-kappa B activation by SN50, a specific NF-kappa B blocker, abolishes silica-induced TNF alpha production. Pretreatment of the cells with catalase (H2O2 scavenger) or def eroxamine (. OH scavenger) effectively inhibits NF-kappa B and TNF alpha ac tivation, whereas superoxide dismutase (O-2(-) scavenger) has an opposite e ffect. These results indicate that silica-mediated free radical generation and NF-kappa B activation play important roles in silica-induced TNF alpha gene expression.