Dibenzoylmethane, a component of licorice, suppresses monocyte-to-macrophage differentiation and inflammatory responses in human monocytes and mouse macrophages

Abstract

The objective of this study was to investigate the effect of dibenzoylmethane (DBM) on monocyte-to-macrophage differentiation, the inflammatory response, and the resulting signaling in human monocytes and murine macrophage. DBM effectively inhibited the monocyte-to-macrophage differentiation induced by phorbol 12-myristate 13-acetate (PMA) through a reduction in adhesion of THP-1 cells. Cluster of differentiation molecule β (CD11β) and CD36, which are surface markers of macrophage differentiation, were downregulated by 80 and 74%, respectively. DBM also significantly inhibited lipopolysaccharide (LPS)-induced nitrite (NO) production through the downregulation of inducible oxide synthase (iNOS) in RAW264.7 cells. The abundance of cyclooxygenase-2 (COX-2), a pro-inflammatory protein, was also effectively decreased by DBM in a dose-dependent manner. DBM (50µM) reduced the levels of COX-2 and iNOS by 81 and 78%, respectively. DBM significantly inhibited the translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), an inflammatory transcription factor, into the nucleus. DBM-mediated increase of NF-κB translocation resulted from the DBM-induced suppression of the phosphorylation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα). In contrast, DBM effectively increased the expression of nuclear factor E2-related factor 2 (Nrf2) and its target protein, hemeoxygenase-1 (HO-1). Nrf2 translocation into the nucleus was also significantly enhanced by DBM. Furthermore, DBM effectively inhibited the expression of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, and monocyte chemoattractant protein-1 (MCP-1). These results indicated that the DBM-mediated differential regulation of NF-κB and Nrf2, which are major transcription factors involved in inflammation, inhibited the expression of inflammatory cytokines.