Anti-inflammatory Activity of Rhamnetin and a Model of Its Binding to c-Jun NH2-Terminal Kinase 1 and p38 MAPK

Rhamnetin (1), a commonly occurring plant O-methylated flavonoid, possesses antioxidant properties. To address the potential therapeutic efficacy of 1, its anti-inflammatory activity and mode of action in mouse macrophage-derived RAW264.7 cells stimulated with lipopolysaccharide (LPS) or interferon (IFN)-gamma were investigated. Rhamnetin (1) suppressed mouse tumor necrosis factor (mTNF)-alpha, mouse macrophage inflammatory protein (mMIP)-1, and mMIP-2 cytokine production in LPS-stimulated macrophages. A nontoxic dose of 1 suppressed nitric oxide production. It was found that the anti-inflammatory effects of 1 are mediated by actions on the p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and cyclooxygenase (COX)-2 pathways in LPS- or IFN-gamma-stimulated RAW264.7 cells. It was determined that 1 binds to human JNK1 (9.7 x 10(8) M-1) and p38 MAPK (2.31 x 10(7) M-1) with good affinity. The binding model showed interactions with the 3'- and 4'-hydroxy groups of the B-ring and the 5-hydroxy group of the A-ring of 1. Further, 1 exerted an anti-inflammatory effect, reducing the levels of pro-inflammatory cytokines and mediators.