Bioactive Constituents from the Roots of Eurycoma longifolia

Four new phenolic components, eurylophenolosides A (1) and B (2), eurylolignanosides A (3) and B (4), along with twelve known compounds were isolated from the roots of Eurycoma longifolia Jack. The structure of these components was elucidated by using various spectral techniques and chemical reactions. Among the known isolates, syringaldehyde (12), 3-chloro-4-hydroxybenzoic acid (13), 3-chloro-4-hydroxyl benzoic acid-4-O-β-d-glucopyranoside (14), and isotachioside (15) were isolated from the Eurycoma genus for the first time. Further, the NMR data of 14 was reported here firstly. Meanwhile, the nitric oxide (NO) inhibitory activities of all compounds were examined in lipopolysaccharide (LPS)-stimulated RAW264.7 cells at 40 μM. As results, piscidinol A (6), 24-epi-piscidinol A (7), bourjotinolone A (10), and scopoletin (16) were found to play important role in suppressing NO levels without cytotoxicity. Furthermore, the Western blot method was used to investigate the mechanism of compounds 6, 7, 10, and 16 by analysing the level of inflammation related proteins, such as inducible nitric oxide synthase (iNOS), interleukin-6 (IL-6), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in LPS-stimulated RAW264.7 cells. Consequently, compounds 6, 7, 10, and 16 were found to significantly inhibit LPS-induced protein expression of IL-6, NF-κB and iNOS in NF-κB signaling pathway. Moreover, it was found that the protein expression inhibitory effects of 6, 7, and 16 exhibited in a dose-dependent manner. The mechanism may be related to the inhibition of the iNOS expressions through suppressing the IL-6-induced NF-κB pathway.