Anti-inflammatory effect of Cortex Eucommiae via modulation of the toll-like receptor 4 pathway in lipopolysaccharide-stimulated RAW 264.7 macrophages

Abstract Ethnopharmocological relevance Cortex Eucommiae (CE), the bark of Eucommia ulmoides Oliv., has been traditionally used for its kidney-tonifying and bone- and tendon-enhancing properties in Korea, China, and Japan. CE has been historically prescribed for inflammatory conditions such as arthritis of the knee and ankle. Aim of the study Although CE has recently been shown to suppress inflammation in scientific studies, whether this effect involves modulation of the toll-like receptor 4 (TLR-4) pathway is currently unknown. Materials and methods The modulatory effect of CE on the TLR-4 pathway, both myeloid differentiation primary response gene 88 (Myd88)-dependent and independent, was investigated through real-time reverse transcriptase-polymerase chain reaction (RT-PCR), western blotting, and a reporter gene assay in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. Results CE dose-dependently inhibited nitric oxide production without significant cytotoxicity with an IC 50 of 356.23 μg/mL. In addition, CE down-regulated both LPS-induced mRNA and protein expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) in a dose-dependent manner. CE suppressed LPS-induced activation of nuclear factor-κB (NF-κB) and the mitogen-activated protein kinase (MAPK) pathways, which together comprise the Myd88-dependent TLR-4 pathway. The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was also down-regulated by CE in a dose-dependent manner. CE additionally suppressed LPS-induced activation of interferon-β (IFN-β) and signal transducer and activator of transcription (STAT) pathway, which is associated with the Myd88-independent TLR-4 pathway. Conclusions CE down-regulated both Myd88-dependent and independent TLR-4 pathways, thus exerting anti-inflammatory effects. These results suggest that CE may be used as a potential therapeutic agent against chronic inflammatory diseases.