Japanese bog orchid (Eupatorium japonicum) extract suppresses expression of inducible nitric oxide synthase and cyclooxygenase-2 induced by toll-like receptor agonists

Toll-like receptors (TLR) play an important role in the recognition of many pathogen-associated molecular patterns and the induction of innate immunity. Dysregulated activation of TLR signaling pathways is associated with certain inflammatory diseases. Japanese bog orchid (Eupatorium japonicum), which belongs to a family of Asteraceae plants, is consumed as a tea. The present study investigated the effect of the ethanol extracts of flowers of Japanese bog orchid (EJE) on nuclear factor (NF)-κB activation and expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) by TLR agonists in murine macrophages. EJE suppressed NF-κB activation and iNOS and COX-2 expression induced by lipopolysaccharide (TLR4 agonist), polyriboinosinic polyribocytidylic acid (TLR3), and macrophage-activating 2 kDa lipopeptide (TLR2 and TLR6). These results suggest that EJE can regulate TLR signaling pathways and indicated its potential as a potent anti-inflammatory drug.