Euscaphic acid isolated from roots of Rosa rugosa inhibits LPS-induced inflammatory responses via TLR4-mediated NF-κB inactivation in RAW 264.7 macrophages

Abstract

As an attempt to search for bioactive natural products exerting anti-inflammatory activity, we have evaluated the anti-inflammatory effects of euscaphic acid (19α-hydroxyursane-type triterpenoids, EA) isolated from roots of Rosa rugosa and its underlying molecular mechanisms in lipopolysaccharide (LPS)-induced RAW 264.7 macrophages. EA concentration-dependently reduced the production of nitric oxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) induced by LPS in RAW 264.7 macgophages. Consistent with these data, expression levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) protein and iNOS, COX-2, TNF-α, and IL-1β mRNA were inhibited by EA in a concentration-dependent manner. In addition, EA attenuated LPS-induced DNA binding and transcriptional activity of nuclear factor-kappa B (NF-κB), which was accompanied by a parallel reduction of degradation and phosphorylation of inhibitory kappa Bα (IκBα) and consequently by decreased nuclear translocation of p65 subunit of NF-κB. Pretreatment with EA significantly inhibited the LPS-induced phosphorylation of IκB kinase β (IKKβ), p38, and JNK, whereas the phosphorylation of ERK1/2 was unaffected. Furthermore, EA interfered with the LPS-induced clustering of TNF receptor-associated factor 6 (TRAF6) with interleukin receptor associated kinase 1 (IRAK1) and transforming growth factor-β-activated kinase 1 (TAK1). Taken together, these results suggest that EA inhibits LPS-induced inflammatory responses by interference with the clustering of TRAF6 with IRAK1 and TAK1, resulting in blocking the activation of IKK and MAPKs signal transduction to downregulate NF-κB activations.