Effect of 5-O-Methylhirsutanonol on Nuclear Factor-κB-Dependent Production of NO and Expression of iNOS in Lipopolysaccharide-Induced RAW264.7 Cells

Diarylheptanoids are known to have anti-inflammatory and anti-atherosclerotic activities in various cell types, including macrophages. 5-O-Methylhirsutanonol (5-MH) isolated from the leaves of Alnus japonica Steud exhibited the antioxidant activities on Cu²⁺- and AAPH-mediated low-density lipoprotein (LDL) oxidation in the thiobarbituric acid-reactive substances (TBARS) assay as well as the macrophage-mediated LDL oxidation. In the main study, we examined anti-inflammatory activities of 5-O-methylhirsutanonol (5-MH) on nuclear factor κB (NF-κB)-dependent nitric oxide (NO) production and expression of inducible nitric oxide synthease (iNOS) in lipopolysaccharide (LPS)-induced RAW264.7 macrophages. 5-MH inhibited NO production with an IC₅₀ value of 14.5 µM and expression of both iNOS protein and iNOS mRNA in a parallel dose–response manner. Then, expression of inflammation-associated genes, such as TNF-α, COX-2, and IL-1β, was suppressed by 5-MH, as determined by reverse transcriptase polymerase chain reaction analysis. Moreover, 5-MH attenuated NF-κB activation by inhibition of hyperphosphorylation of IκB-α and its subsequent proteolytic degradation and p65 nuclear translocation, as well as preventing DNA-binding ability. In addition, 5-MH suppressed the mRNA expression of the gene reactive oxygen species (ROS) concerned in the regulation of NF-κB signaling.