Anti-inflammatory effect of flavonoids isolated from Korea Citrus aurantium L. on lipopolysaccharide-induced mouse macrophage RAW 264.7 cells by blocking of nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signalling pathways

Citrus fruits are an abundant source of various flavonoids, which have been used as a traditional herbal medicine in Korea and China. Most flavonoids are known to have anti-oxidant, anti-bacterial and analgesic properties. In this study, it was examined whether flavonoids (nobiletin, naringin and hesperidin) isolated from Korea Citrus aurantium L. inhibited the pro-inflammatory mediators including cytokines by blocking nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signalling in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. The flavonoids suppressed mRNA and protein expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in LPS-induced macrophages. The molecular mechanism was associated with inhibition of the degradation/phosphorylation of I-κB-α and nuclear translocation of the NF-κB p-65 as well as phosphorylation of MAPK by flavonoids. These results suggest that flavonoids have anti-inflammatory effects by suppressing expression of COX-2, iNOS and cytokines by blocking the NF-κB and MAPK signalling in RAW 264.7 macrophages.