Nicotine Reduces TNF-alpha Expression Through a alpha 7 nAChR/MyD88/NF-kappa B Pathway in HBE16 Airway Epithelial Cells

Aims: To explore the signaling mechanism associated with the inhibitory effect of nicotine on tumor necrosis factor (TNF)-alpha expression in human airway epithelial cells. Methods: HBE16 airway epithelial cells were cultured and incubated with either nicotine or cigarette smoke extract (CE). Cells were then transfected with alpha 1, alpha 5, or alpha 7 nicotinic acetylcholine receptor (nAChR)-specific small interfering RNAs (siRNAs). The effects of nicotine on the production of proinflammatory factors TNF-alpha, in transfected cells were analyzed. Furthermore, we assayed the expression levels of myeloid differentiation primary response gene 88 (MyD88) protein, nuclear factor kappa-lightchain- enhancer of activated B cells (NF-kappa B) p65 protein, NF-kappa B activity and NF-kappa B inhibitor alpha (I-kappa B alpha) expression in cells after treatment with nicotine or alpha 7 nAChR inhibitor, alpha-bungarotoxin (alpha-BTX). Results: The production of TNF-alpha was lower in cells pretreated with nicotine before lipopolysaccharide (LPS) stimulation, compared with LPS-only-treated cells. In contrast, in alpha 7 siRNA-transfected cells incubated with nicotine and LPS, TNF-alpha expression was higher than that in non-transfected cells or in alpha 1 or alpha 5 siRNAtransfected cells. Addition of MyD88 siRNA or the NF kappa B inhibitor pyridine-2,6-dithiocarboxylic acid (PDTC) also reduced TNF-alpha expression. Furthermore, we found that nicotine decreased MyD88 protein, NF-kappa B p65 protein, NF-kappa B activity and phospho-I-kappa B alpha expression induced by CE or LPS. The inhibitor alpha-BTX could reverse these effects. Conclusion: Nicotine reduces TNF-alpha expression in HBE16 airway epithelial cells, mainly through an alpha 7 nAChR/MyD88/NF-kappa B pathway. Copyright (C) 2011 S. Karger AG, Basel