Brassinin, a phytoalexin in cruciferous vegetables, suppresses obesity‐induced inflammatory responses through the Nrf2‐HO‐1 signaling pathway in an adipocyte‐macrophage co‐culture system

The aim of this study was to investigate the effect of brassinin (BR), a phytoalexin found in plants belonging to the Brassicaceae family, on the obesity‐induced inflammatory response and its molecular mechanism in co‐culture of 3T3‐L1 adipocytes and RAW264.7 macrophages. BR effectively suppressed lipid accumulation by down‐regulating the expression of adipogenic factors, which in turn, were regulated by early adipogenic factors such as CCAAT‐enhancer‐binding protein‐β and Kruppel‐like factor 2. Production of inflammatory cytokines and reactive oxygen species, induced by adipocyte‐conditioned medium, was significantly decreased in BR‐treated cells. This effect of BR was more prominent in contact co‐culture of adipocytes and macrophages with a 90% and 34% reduction in IL‐6 and MCP‐1 levels, respectively. BR also restored adiponectin expression, which was significantly reduced by culturing adipocytes in macrophage‐conditioned medium. In the transwell system, BR increased the protein levels of nuclear factor (erythroid‐derived 2)‐like 2 (Nrf2) and its target molecule, hemoxygenase‐1 (HO‐1), by 55%–93% and 45%–48%, respectively, and also increased Nrf2 translocation into the nucleus. However, knockdown of Nrf2 or HO‐1 in RAW264.7 cells restored this BR‐mediated inhibition of IL‐6 and MCP‐1 production. These results indicated that BR inhibited obesity‐induced inflammation via the Nrf2‐HO‐1 pathway.