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4‐(Methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone, a component of tobacco smoke, modulates mediator release from human bronchial and alveolar epithelial cells

Respiratory epithelial cells are known to contribute to immune responses through  the  release  of  mediators.  The  aim  of  this  study  was  to  characterize the immunomodulatory effects of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK), a tobacco carcinogen, on respiratory epithelial cells and to compare two metabolic pathways, α‐methylhydroxylation and α‐methylenehydroxylation, involved in these effects using selective precursors, 4‐(acetoxy‐methylnitrosamino)‐1‐(3‐pyridil)‐1‐butanone (NNKOAc) and N‐nitroso (acetoxymethyl) methylamine (NDMAOAc), respectively. Human bronchial and alveolar epithelial cell lines, BEAS‐2B and A549, respectively, were treated with NNK, NNKOAc and NDMAOAc for 24 h with and without tumour necrosis factor (TNF) and mediators released in cell‐free supernatants were measured by enzyme‐linked immunosorbent assay (ELISA). NNK significantly inhibited interleukin (IL)‐8, IL‐6 and monocyte chemoattractant protein‐1 (MCP‐1) production in both cell types. Similar results were observed with primary bronchial and alveolar epithelial cells. Although NNK increased prostaglandin E2 (PGE2) production by A549 cells, its immunomodulatory effects were not mediated by PGE2 according to the results with cyclo‐oxygenase inhibitors. NNKOAc mimicked NNK effects, whereas NDMAOAc significantly inhibited IL‐8 production in BEAS‐2B cells and MCP‐1 in both cell types. These results demonstrate that NNK and its reactive metabolites have immunosuppressive effects on respiratory epithelial cells, which could contribute to the increased respiratory infections observed in smokers and the development and/or the progression of lung cancer.