The effects of cardamonin on lipopolysaccharide-induced inflammatory protein production and MAP kinase and nFkappaB signalling pathways in monocytes/macrophages

Background and purpose: In this study we examined the effect of the natural product cardamonin, upon lipopolysaccharide (LPS)-induced inflammatory gene expression in order to attempt to pinpoint the mechanism of action. Experimental approaches: Cardamonin was isolated from the Greek plant A. absinthium L. Its effects were assessed on LPSinduced nitrite release and iNOS and COX-2 protein expression in two macrophage cell lines. Western blotting was used to investigate its effects on phosphorylation of the mitogen activated protein (MAP) kinases, ERK, JNK and p38 MAP kinase, and activation of the NFkB pathway, at the level of IkBa degradation and phosphorylation of NFkB. Also its effects on NFkB and GAS/GAF-DNA binding were assessed by EMSA. Key results: Cardamonin concentration-dependently inhibited both NO release and iNOS expression but had no effect on COX-2 expression. It did not affect phosphorylation of the MAP kinases, degradation of IkBa or phosphorylation of NFkB. However, it inhibited NFkB DNA-binding in both LPS-stimulated cells and nuclear extracts of the cells (in vitro). It also inhibited IFNg-stimulated iNOS induction and GAS/GAF-DNA binding. Conclusions and implications: These results show that the inhibitory effect of cardamonin on LPS-induced iNOS induction is not mediated via effects on the initial activation of the NFkB or MAP kinase pathways but is due to a direct effect on transcription factor binding to DNA. However, although some selectivity in cardamonin’s action is implicated by its inability to affect COX-2 expression, its exact mechanism(s) of action has yet to be identified.