Inhibitory Mechanisms of Water Extract of Oplopanax elatus on Lipopolysaccharide-Induced Inflammatory Responses in RAW 264.7 Murine Macrophage Cells

Objective To study the anti-inflammatory action and cellular mechanism of Oplopanax elatus . Methods A hot water extract of OE (WOE) was prepared and a major constituent, syringin, was successfully isolated. Its content in WOE was found to be 214.0 µg/g dried plant (w/w). Their anti-inflammatory activities were examined using RAW 264.7 macrophages and a mouse model of croton oil-induced ear edema. Results In lipopolysaccharide (LPS)-treated RAW 264.7 cells, a mouse macrophage cell line, WOE was found to significantly and strongly inhibit cyclooxygenase-2 (COX-2)-induced prostaglandin E 2 (PGE 2 ) production [half maximal inhibitory concentration (IC 50 )=135.2 µg/mL] and inducible nitric oxide synthase (iNOS)-induced NO production (IC 50 =242.9 µg/mL). In the same condition, WOE was revealed to inhibit NO production by down-regulating iNOS expression, mainly by interrupting mitogen activated protein kinases (MAPKs)/activator protein-1 (AP-1) pathway. The activation of all three major MAPKs, p38 MAPK, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase, was inhibited by WOE (50–300 µg/mL). On the other hand, WOE reduced PGE 2 production by inhibiting COX-2 enzyme activity, but did not affect COX-2 expression levels. In addition, WOE inhibited the production of proinflammatory cytokines such as interleukin-6 and tumor necrosis factor-α. In croton oil-induced ear edema in mice, oral administration of WOE (50–300 mg/kg) dose-dependently inhibited edematic inflammation. Conclusion Water extract of OE exhibited multiple anti-inflammatory action mechanisms and may have potential for treating inflammatory disorders.