Apocynin Suppresses Lipopolysaccharide-Induced Inflammatory Responses Through the Inhibition of MAP Kinase Signaling Pathway in RAW264.7 Cells.

Apocynin, an inhibitor of NADPH oxidase, exhibits anti-inflammatory properties in ulcerative colitis. However, the underlying mechanism by which apocynin exerts this effect has not been clearly demonstrated. The objective of this study was to elucidate the anti-inflammatory mechanism of apocynin in lipopolysaccharide (LPS)-challenged RAW264.7 macrophage cells. Apocynin inhibited LPS-induced extracellular secretion of the pro-inflammatory mediators, nitric oxide (NO) and PGE2 and the expression of inducible nitric oxide synthase and cyclooxygenase-2. Apocynin also suppressed LPS-induced secretion of the pro-inflammatory cytokine, tumor necrosis factor-α and LPS-induced degradation of IκB, which retains NF-κB in the cytoplasm, consequently inhibiting the transcription of pro-inflammatory genes by NF-κB in the nucleus. To elucidate the underlying anti-inflammatory mechanism of apocynin, the involvement of the mitogen-activated protein (MAP) kinases, c-jun N-terminal kinase, extracellular signal-regulated kinases, and p38 was examined. Apocynin attenuated LPS-induced activation of all three MAP kinases in a concentration-dependent manner. The present study demonstrates apocynin exerts anti-inflammatory activity via the suppression of MAP kinase signaling pathways in LPS-challenged RAW264.7 macrophage cells. Drug Dev Res, 2016.