IVSE, isolated from Inula japonica,suppresses LPS-induced NO production via NF-κB and MAPK inactivation in RAW264.7 cells

Our previous study showed that the extract of Inula japonica Thunb. (I. japonica) has anti-inflammatory and anti-asthmatic activities. In an attempt to find anti-inflammatory compounds from I. japonica, we recently isolated 1,6α-dihydroxy-4αH-1,10-secoeudesma-5(10),11(13)-dien-12,8β-olide (SE), 6α-isobutyryloxy-1-hydroxy-4αH-1,10-secoeudesma-5(10),11(13)-dien-12,8β-olide (IBSE), and 6α-isovaleryloxy-1-hydroxy-4αH-1,10-secoeudesma-5(10),11(13)-dien-12,8β-olide (IVSE) from the extract of I. japonica, and investigated their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW264.7 cells.The inhibitory effect of IVSE, SE and IBSE on NO production in LPS-induced RAW264.7 cells was examined using Griess reagent, and the effects of IVSE on the expressions of inducible nitric oxide synthase (iNOS) and its upstream signal proteins including IκB kinase (IKK)/inhibitor kappa B (IκB)-α/nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) were investigated by Western blot.Among the 3 compounds isolated, SE, IBSE, and IVSE inhibited NO production at 2.5 μM with 5.1%, 40.4%, and 52.8%, respectively. IVSE displayed the most potent inhibition of NO production. Mechanism analysis indicated that IVSE dramatically decreased the expression of iNOS, reduced the translocation of the NF-κB subunit p65 into the nucleus by interrupting the phosphorylation and degradation of IκB-α, and inhibited the activation of the upstream mediator IKK α/β. Furthermore, our results showed that IVSE inhibited the phosphorylation of MAPKs including extracellular regulated kinases (ERK1/2), c-Jun N-terminal kinases (JNK) and p38.IVSE exhibited anti-inflammatory activity by inhibiting NO production, in which inactivation of NF-κB and MAPKs might be involved. Our results suggest that IVSE might become an anti-inflammatory drug candidate.