Alantolactone suppresses inducible nitric oxide synthase and cyclooxygenase-2 expression by down-regulating NF-κB, MAPK and AP-1 via the MyD88 signaling pathway in LPS-activated RAW 264.7 cells

Several sesquiterpene lactones are the active components of several medicinal plants and have been demonstrated to perform various pharmacological functions. In this study, we investigated the anti-inflammatory effects of alantolactone, a sesquiterpene lactone isolated from the root of Aucklandia lappa, in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells and peritoneal macrophages. Alantolactone inhibited inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) protein and mRNA transcription, as well as the downstream products, nitric oxide (NO), prostaglandin E(2) (PGE(2)) and tumor necrosis factor-α (TNF-α). Investigation of the effects on nuclear factor κB (NF-κB) signaling showed that alantolactone inhibits the phosphorylation of inhibitory κB (IκB)-α and IκB kinase (IKK) and the subsequent translocation of the p65 and p50 NF-κB subunits to the nucleus. Moreover, inhibition of mitogen-activated protein kinases (MAPKs), including c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38 MAPK, and activator protein-1 (AP-1) was also observed. A further study indicated that alantolactone attenuated the phosphorylation of Akt and inhibited the expression of MyD88 and Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP), an upstream signaling molecule required for IKK and MAPKs activation. Taken together, these results suggest that alantolactone exerts its anti-inflammatory effect in LPS-stimulated RAW 264.7 cells by suppressing NF-κB activation and MAPKs phophorylation via downregulation of the MyD88 signaling pathway. Thus, alantolactone may provide a useful therapeutic approach for inflammation-associated diseases.