Glucocorticoid receptor agonist compound K regulates Dectin-1-dependent inflammatory signaling through inhibition of reactive oxygen species.

Abstract Aims Compound K (C-K; 20-O- d -glucopyranosyl-20(S)-protopanaxadiol) is a functional ligand of the glucocorticoid receptor (GR) and regulates toll-like receptor-4-dependent inflammation. Here, the role of C-K in the regulation of zymosan-mediated inflammation was investigated in murine bone marrow-derived macrophages and the murine macrophage cell line RAW264.7. Main methods The in vitro regulatory effects of C-K on zymosan-induced cytokine production were measured by enzyme-linked immunosorbent assay. Phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, p38, and p47phox was determined by detection of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase cytosolic subunit by Western blotting. The generation of reactive oxygen species (ROS) was assayed using specific immunofluorescent dyes. NADPH oxidase activities were measured by luminometric analysis. The histopathology of mouse livers and spleens was evaluated immunohistochemically. Dexamethasone, a well-known GR agonist, was used to study the effects of C-K. Key findings Pre-treatment with C-K significantly inhibited zymosan-mediated secretion of tumor necrosis factor-α, interleukin (IL)-6, and IL-12 p40, and the activation of ERK1/2 and p38. C-K also markedly suppressed zymosan-mediated superoxide generation, NADPH oxidase activities, and Ser345-p47phox phosphorylation in macrophages. Blockade of Dectin-1 profoundly attenuated the inhibitory effects of C-K in zymosan-induced inflammation and ROS generation by macrophages. The in vivo administration of C-K significantly rescued cells from zymosan-induced lethal shock through inhibition of systemic inflammatory cytokine production. Significance The ability of C-K to regulate zymosan-induced inflammation through Dectin-1 suggests a novel approach for the control of excessive lethal inflammation.