9,10-Dihydro-2,5-dimethoxyphenanthrene-1,7-diol, from Eulophia ochreata, inhibits inflammatory signalling mediated by Toll-like receptors

Background and purpose:

9,10-Dihydro-2,5-dimethoxyphenanthrene-1,7-diol (RSCL-0520) is a phenanthrene isolated from Eulophia ochreata, one of the Orchidaceae family, known by local tradition to exhibit medicinal properties. However, no anti-inflammatory activity or any molecular mechanisms involved have been reported or elucidated. Here, for the first time, we evaluate the anti-inflammatory properties of RSCL-0520 on responses induced by lipopolysaccharide (LPS) and mediated via Toll-like receptors (TLRs).

Experimental approach:

The in vitro anti-inflammatory activities of RSCL-0520 were investigated in LPS-stimulated monocytic cells, measuring activation of cytokine and inflammatory genes regulated by nuclear factor-κB (NF-κB). Tumour necrosis factor (TNF)-α levels in serum following LPS stimulation in mice and carrageenan-induced paw oedema in rats were used as in vivo models.

Key results:

Pretreatment with RSCL-0520 effectively inhibited LPS-induced, TLR4-mediated, NF-κB-activated inflammatory genes in vitro, and reduced both LPS-induced TNF-α release and carrageenan-induced paw oedema in rats. Treatment with RSCL-0520 reduced LPS-stimulated mRNA expression of TNF-α, COX-2, intercellular adhesion molecule-1, interleukin (IL)-8 and IL-1β, all regulated through NF-κB activation. RSCL-0520, however, did not interfere with any cellular processes in the absence of LPS.

Conclusions and implications:

RSCL-0520 blocked signals generated by TLR4 activation, as shown by down-regulation of NF-κB-regulated inflammatory cytokines. The inhibitory effect involved both MyD88-dependent and -independent signalling cascades. Our data elucidated the molecular mechanisms involved, and support the search for plant-derived TLR antagonists, as potential anti inflammatory agents.