Anti-neuroinflammatory effects of tryptanthrin from Polygonum tinctorium Lour. in lipopolysaccharide-stimulated BV2 microglial cells

This study was conducted to isolate the anti-neuroinflammatory component(s) in the 80% EtOH extract of P. tinctoria, and to investigate underlying molecular mechanism of the anti-neuroinflammatory component(s) in LPS-induced BV2 microglial cells. To isolate the active component(s) in the extract, various chromatographic methods were employed, and the structures of the isolated secondary metabolites were determined mainly by analysis of spectroscopic data such as NMR and MS data. Tryptanthrin (1), isolated from P. tinctoria extract, significantly inhibited the protein expression of iNOS and COX-2, and reduced the levels of their products (NO and PGE2) in LPS-stimulated BV2 microglial cells. Tryptanthrin (1) also downregulated the production of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-1β. These anti-neuroinflammatory effects of tryptanthrin (1) was elucidated to be correlated with inactivating NF-κB pathway by interrupting the phosphorylation and degradation of the inhibitor of κB-α protein, and inhibiting the DNA binding activity of NF-κB. In addition, tryptanthrin (1) suppressed the activation of p38 MAPK pathway. Furthermore, tryptanthrin (1) inhibited the TLR4 and MyD88 protein expression in LPS-stimulated BV2 microglial cells. Taken together, it was suggested that tryptanthrin (1) have anti-neuroinflammatory effect by regulating TLR4-MyD88-mediated several inflammatory pathways including p38 and NF-κB pathways in LPS-induced BV2 microglial cells.