Suppression of methylmercury-induced IL-6 and MCP-1 expressions by N-acetylcysteine in U-87MG human astrocytoma cells

AimsThe aim of this study was to clarify the involvement of oxidative stress in methylmercury (MeHg)-induced pro-inflammatory cytokine expressions and the suppressive effects of N-acetylcysteine (NAC) in MeHg-induced cytokine expression.Materials and methodsUsing U-87-MG human astrocytoma cell line, interleukin (IL)-6 and monocyte chemoattractant protein (MCP)-1 expressions induced by 4 μM MeHg were measured at mRNA and protein levels. Hydrogen peroxide (H2O2) and superoxide anion (O2−) were quantified by flow-cytometry analysis. To examine the suppressive effects of NAC on the cytokine expressions among different timing of NAC treatment, cells were treated with 0.5 or 5 mM NAC before, simultaneously, or after MeHg administration.Key findingsMeHg exposure at 4 μM, a non-cytotoxic concentration, significantly induced MCP-1 and IL-6 expressions at both mRNA and protein levels. A significant increase of H2O2 production but not O2− was observed. MeHg-induced expression of MCP-1 and IL-6 mRNA was reduced by 10–20% in the presence of 5 mM NAC (co-treatment experiment) compared to cells treated with MeHg only. Pre-treatment of cells with 0.5 or 5 mM NAC at 0.5 or 1 h and its subsequent washout before MeHg addition suppressed MCP-1 and IL-6 cytokine expressions. Post-treatment of cells with NAC after MeHg addition also suppressed the cytokine induction, but the magnitude of suppression was evidently lower than in co-treated cells even though the H2O2 generation was almost completely suppressed by NAC.SignificanceNAC may effectively suppress the MeHg-induced cytokine production through both, inhibition of reactive oxygen species as well as extracellular chelation of MeHg in astrocytes.