Critical role of glass fiber length in TNF-alpha production and transcription factor activation in macrophages.

Recent studies have demonstrated that dielectrophoresis is an efficient method for the separation of fibers according to fiber length. This method allows the investigation of fiber-cell interactions with fiber samples of the same composition but of different lengths. In the present study, we analyzed the effects of length on the interaction between glass fibers and macrophages by focusing on production of the inflammatory cytokine tumor necrosis factor (TNF)-alpha in a mouse macrophage cell line (RAW 264.7). The underlying molecular mechanisms controlling TNF-alpha production were investigated at the gene transcription level. The results show that glass fibers induced TNF-alpha production in macrophages and that this induction was associated with activation of the gene promoter. Activation of the transcription factor nuclear factor (NF)-kappaB was responsible for this induced promoter activity. The inhibition of both TNF-alpha production and NF-kappaB activation by N-acetyl-L-cysteine, an antioxidant, indicates that generation of oxidants may contribute to the induction of this cytokine and activation of this transcription factor by glass fibers. Long fibers (17 micrometer) were significantly more potent than short fibers (7 micrometer) in inducing NF-kappaB activation, the gene promoter activity, and the production of TNF-alpha. This fiber length-dependent difference in the stimulatory potency correlated with the fact that macrophages were able to completely engulf short glass fibers, whereas phagocytosis of long glass fibers was incomplete. These results suggest that fiber length plays a critical role in the potential pathogenicity of glass fibers.