Lignans from Saururus chinensis exhibit anti-inflammatory activity by influencing the Nrf2/HO-1 activation pathway

As part of our ongoing program to develop anti-inflammatory agents, an extract derived from Saururus chinensis collected in Korea was found to inhibit nitric oxide (NO) production in RAW264.7 cells. Bioassay-guided fractionation led to the isolation two new (1 and 2) and six known dineolignans (3-8). To the best of our knowledge, manassatin B₁ (3) was isolated from S. chinensis for the first time. All structures were elucidated using extensive spectroscopic analysis. Of these compounds, 2 and 8 inhibited lipopolysaccharide (LPS)-induced production of NO and showed IC₅₀ values of 5.80 and 1.52 µM, respectively. LPS-induced expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) was also significantly suppressed by the administration of 2 and 8. In addition, these lignans induced the expression of heme oxygenase-1 (HO-1) in a concentration-dependent manner. Nuclear translocation of nuclear-E2-related factor 2 (Nrf2), a key regulator of HO-1 protein expression, was also induced in RAW264.7 cells treated with 2 and 8. These findings suggested that these lignans exerted anti-inflammatory effects in RAW264.7 cells through modulation of the Nrf2/HO-1 pathway and that they were potential HO-1 inducers for preventing or treating inflammation.