Zingiberaceous and Citrus Constituents, 1'-Acetoxychavicol Acetate, Zerumbone, Auraptene, and Nobiletin, Suppress Lipopolysaccharide-Induced Cyclooxygenase-2 Expression in RAW264.7 Murine Macrophages through Different Modes of Action

In the present study, we explored the suppressive activities of 1'-acetoxychavicol acetate (ACA), auraptene, nobiletin, and zerumbone toward LPS-induced cyclooxygenase (COX)-2 mRNA expression in mouse macrophages and the underlying molecular mechanisms. Pretreatment of RAW264.7 cells with LPS led to the activation of mitogen-activated protein kinase (MAPK)s [p38, extracellular signal-regulated kinase (ERK)1/2, c-Jun NH2-terminal kinase (JNK)1/2] and Akt, together with degradation of the inhibitor of nuclear factor-[kappa]B (I[kappa]B)-[alpha] protein and nuclear translocation of nuclear factor (NF)-[kappa]B p65, and the resultant activation of activator protein (AP)-1, NF-[kappa]B, and cAMP-responsive element-binding protein (CREB) transcription factors. ACA abrogated ERK1/2 and JNK1/2, but not p38 MAPK, as well as the activation of those transcription factors. Although it allowed LPS-triggered phosphorylation of those MAPKs and NF-[kappa]B nuclear translocation, nobiletin suppressed the activation of AP-1, NF-[kappa]B, and CREB. Zerumbone had no effect on those transcription factors, though it attenuated COX-2 mRNA expression, suggesting that it disrupts the stabilization of COX-2 mRNA. Conversely, zerumbone significantly accelerated spontaneous COX-2 mRNA decay, the potency of which was comparable with that of SB203580, an inhibitor of p38 MAPK, whose activation has key roles in the proinflammatory mRNA stabilization processes. Because SB203580 but not zerumbone suppressed LPS-induced p38 MAPK activation, the molecular targets of zerumbone may be MAPK-activated protein kinase-2 or located downstream. However, auraptene suppressed the expression of COX-2 protein but not mRNA, implying that it targets translation. We propose that these phytochemicals are promising chemopreventive agents for inflammation-associated carcinogenesis. Their use in combination may enhance their efficacy because of their different modes of action.