Desoxyrhapontigenin up-regulates Nrf2-mediated heme oxygenase-1 expression in macrophages and inflammatory lung injury

Heme oxygenase-1 (HO-1) is an important anti-inflammatory, antioxidative and cytoprotective enzyme that is regulated by the activation of the major transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In the present study, six stilbene derivatives isolated from Rheum undulatum L. were assessed for their antioxidative potential. In the tert-butylhydroperoxide (t-BHP)-induced RAW 264.7 macrophage cell line, desoxyrhapontigenin was the most potent component that reduced intracellular reactive oxygen species (ROS) and peroxynitrite. In response to desoxyrhapontigenin, the mRNA expression levels of antioxidant enzymes were up-regulated. An electrophoretic mobility shift assay (EMSA) confirmed that desoxyrhapontigenin promoted the DNA binding of Nrf2 and increased the expression of antioxidant proteins and enzymes regulated by Nrf2. Further investigation utilizing specific inhibitors of Akt, p38, JNK and ERK demonstrated that the phosphatidylinositol 3-kinase (PI3K)/Akt pathway mediates HO-1 expression. Moreover, the increase in Nrf2 expression mediated by treatment with desoxyrhapontigenin was reversed by Nrf2 or Akt gene knock-down. In the LPS-induced in vivo lung inflammation model, pretreatment with desoxyrhapontigenin markedly ameliorated LPS-induced lung inflammation and histological changes. Immunohistochemical analysis of Nrf2, HO-1 and p65 was conducted and confirmed that treatment with desoxyrhapontigenin induced Nrf2 and HO-1 expression but reduced p65 expression. These findings suggest that desoxyrhapontigenin may be a potential therapeutic candidate as an antioxidant or an anti-inflammatory agent.