Regulation of lipopolysaccharide-mediated interleukin-1β release by N-acetylcysteine in THP-1 cells

Abstract

Increased levels of inflammatory cytokines such as interleukin (IL)-1 and IL-8 occur in the bronchoalveolar lavage fluid in various lung diseases. Cytokine gene expression is controlled by transcription factors such as nuclear factor-κB (NF-κB) which can be activated by a number of stimuli including the oxidants prevent. It was hypothesized that lipopolysaccharide (LPS)-induced IL-1β secretion may be modulated by the intracellular thiol redox status of the cells. The effect of the antioxidant compound, N-acetyl-L-cysteine (NAC), on IL-1β release and regulation of NF-κB in a human myelo-monocytic cell line (THP-1) differentiated into macrophages was studied. LPS (10 μg·mL-1) increased IL-1β release at 24 h compared to control levels (p<0.001). NAC (5 mM) also enhanced LPS-induced IL-1β release from THP-1 cells (p<0.001). In addition, treatment of cells with cycloheximide, an inhibitor of protein synthesis, inhibited the NAC-mediated IL-1β release. Under the same conditions, NF-κB binding was activated by LPS and NAC increased this LPS-mediated effect. Western blot analysis revealed that NAC treatment leads to an increase in p50 and p65 protein synthesis. These data indicate that N-acetyl-L-cysteine modulates interleukin-1β release by increasing levels of the homo- and heterodimeric forms of nuclear factor-κB.