Iristectorigenin C suppresses LPS-induced macrophages activation by regulating mPGES-1 expression and p38/JNK pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been used clinically to treat inflammatory diseases clinically. However, the adverse effects of NSAIDs cannot be ignored. Therefore, it is critical for us to find alternative anti-inflammatory drugs that can reduce adverse reactions to herbal medicine, such as Iris tectorum Maxim., which has therapeutic effects and can treat inflammatory diseases and liver-related diseases.

This study aimed to isolate active compounds from I. tectorum and investigate their anti-inflammatory effects and action mechanisms.

Fourteen compounds were isolated from I. tectorum using silica gel column chromatography, Sephadex LH-20, ODS and high performance liquid chromatography, and their structures were identified by examining physicochemical properties, ultraviolet spectroscopy, infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance spectroscopy. Classical inflammatory cell models were established using lipopolysaccharide (LPS)-stimulated RAW264.7 cells and rat primary peritoneal macrophages to examine the effect of these compounds. To examine the action mechanisms, the nitric oxide (NO) levels were measured by Griess reagent and the levels of inflammatory cytokines in the supernatant were measured by ELISA; The expressions of major proteins in prostaglandin E₂ (PGE₂) synthesis and the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways were examined by Western blotting, and the mRNA expression levels were measured by quantitative real-time polymerase chain reaction; and the nuclear translocation of p65 was examined by high content imaging. Molecular docking was used to predict the binding of active compound to target protein.

Our findings revealed that Iristectorigenin C (IT24) significantly inhibited the levels of NO and PGE₂ without affecting cyclooxygenase (COX)-1/COX-2 expression in LPS-induced RAW264.7 cells and rat peritoneal macrophages. Furthermore, IT24 was shown to decrease the expression of microsomal prostaglandin synthetase-1 (mPGES-1) in LPS-induced rat peritoneal macrophages. IT24 did not suppress the phosphorylation and nuclear translocation of proteins in the NF-κB pathway, but it inhibited the phosphorylation of p38/JNK in LPS-stimulated RAW264.7 cells. Additionally, molecular docking analysis indicated that IT24 may directly bind to the mPGES-1 protein.

IT24 might inhibit mPGES-1 and the p38/JNK pathway to exert its anti-inflammatory effects and could be also developed as an inhibitor of mPGES-1 to prevent and treat mPGES-1-related diseases, such as inflammatory diseases, and holds promise for further research and drug development.