Oleuropein suppresses LPS-induced inflammatory responses in RAW 264.7 cell and zebrafish

Oleuropein is one of the primary phenolic compounds present in olive leaf. In this study, the anti-inflammatory effect of oleuropein was investigated using lipopolysaccharide (LPS)-stimulated RAW 264.7 and a zebrafish model. The inhibitory effect of oleuropein on LPS-induced NO production in macrophages was supported by the suppression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In addition, our enzyme immunoassay showed that oleuropein suppressed the release of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and interleukin-6 (IL-6). Oleuropein inhibited the translocation of p65 by suppressing phosphorylation of inhibitory kappa B-α (IκB-α). Oleuropein also decreased activation of ERK1/2 and JNK, which are associated with LPS-induced inflammation, and its downstream gene of AP-1. Furthermore, oleuropein inhibited LPS-stimulated NO generation in a zebrafish model. Taken together, our results demonstrated that oleuropein could reduce inflammatory responses by inhibiting TLR and MAPK signaling, and may be used as an anti-inflammatory agent.