Demethoxycurcumin, a natural derivative of curcumin attenuates LPS-induced pro-inflammatory responses through down-regulation of intracellular ROS-related MAPK/NF-kappaB signaling pathways in N9 microglia induced by lipopolysaccharide

Abstract

Our previous report has showed that demethoxycurcumin (DMC), a natural derivative of curcumin (Cur), exhibited stronger inhibitory activity on nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha) production compared with Cur in lipopolysaccharide (LPS) activated rat primary microglia. In the present study, the effect and possible mechanism of DMC on the production of pro-inflammatory mediators in LPS-activated N9 microglial cells were further investigated. The results showed that DMC significantly suppressed the NO production induced by LPS in N9 microglial cells through inhibiting the protein and mRNA expression of inducible NO synthase (iNOS). DMC also decreased LPS-induced TNF-alpha and IL-1beta expression at both transcriptional and protein level in a concentration-dependent manner. Further studies revealed that DMC blocked IkappaBalpha phosphorylation and degradation, inhibited the phosphorylation of mitogen-activated protein kinases (MAPKs). Moreover, the level of intracellular reactive oxygen species (iROS) was significantly increased by LPS, which is mainly mediated by the up-regulated expression of gp91phox, the catalytic subunit of nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase. Both DMC and Cur could markedly decrease iROS production and the expression of NADPH oxidase induced by LPS, with more potent inhibitory activity of DMC. In summary, these data suggest that DMC exerts its in vitro anti-inflammatory effect in LPS-activated N9 microglial cells by blocking nuclear factor-kappaB (NF-kappaB) and MAPKs activation, which may be partly due to its potent down-regulation of the NADPH-derived iROS production.