Eicosanoid modulation by the short‐chain fatty acid n‐butyrate in human monocytes

n‐Butyrate deriving from bacterial fermentation in the mammalian intestine is a key determinant in gastrointestinal homeostasis. We examined the effects of this short‐chain fatty acid and Toll‐like receptor 2 (TLR) and TLR4 engagement on inflammatory/immunity‐associated genes, cyclo‐oxygenases (COXs), prostaglandins (PGs) and leukotrienes (LTs) in human monocytes. Before RNA isolation, freshly isolated human monocytes were co‐incubated for different time‐points with 1 mm n‐butyrate alone or in combination with bacterial stimuli. Based on a knowledge‐driven approach, a signature of 180 immunity/inflammation‐associated genes was picked and real‐time PCR analysis was performed. Pathway analysis was carried out using a web‐based database analysing program. Based on these gene expression studies the findings were evaluated at the protein/mediator level by Western blot analysis, FACS and ELISA. Following co‐incubation with n‐butyrate and lipopolysaccharide, key enzymes of the eicosanoid pathway, like PTGS2 (COX‐2), TXS, ALOX5, LTA4H and LTC4S, were significantly up‐regulated compared with stimulation with lipopolysaccharide alone. Furthermore, release of the lipid mediators PGE₂, 15d‐PGJ_2, LTB₄ and thromboxane B₂ was increased by n‐butyrate. Regarding signalling, n‐butyrate had no additional effect on mitogen‐activated protein kinase and interfered differently with early and late phases of nuclear factor‐κB signalling. Our results suggest that among many other mediators of eicosanoid signalling n‐butyrate massively induces PGE₂ production by increasing the expression of PTGS2 (COX‐2) in monocytes following TLR4 and TLR2 activation and induces secretion of LTB₄ and thromboxane B₂. This underscores the role of n‐butyrate as a crucial mediator of gut‐specific immunity.