Tectorigenin and irigenin inhibit lipopolysaccharide-induced nitric oxide synthase expression in murine macrophages

Background: Belamcanda chinensis is a common traditional Chinese medicine, which is mainly used for the treatment of respiratory system disorders, including bronchial asthma, tonsillitis and infantile cough. Isoflavonoids, extracted from the rhizome of this plant, have been shown to exert antiinflammatory effects in vitro. In the present study, we evaluated the protective anti-inflammatory effects of tectorigenin and irigenin in Lipopolysaccharide (LPS)-stimulated murine macrophages. Materials and methods: RAW264.7 macrophages were treated with varying concentrations of tectorigenin and irigenin prior to being stimulated with or without LPS. The levels of inflammatory cytokines (Interleukin (IL)-6, Prostaglandin E2 (PGE2), and Tumor Necrosis Factor-alpha (TNF-α)) and mediators (Nitric Oxide (NO)) in the culture supernatant were measured by ELISA and Griess reagent assay, respectively. The cell viability was assessed using the MTT assay and the expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 was analysed by western blotting. Results: The data demonstrated that LPS induced the expression of the inflammatory mediators; whereas, tectorigenin and irigenin suppressed the release of NO, IL-6, PGE-2 and TNF-α in the supernatant of LPS-stimulated macrophages, and inhibited iNOS and COX-2 in a dose dependent manner. Furthermore, we found that these extracts had no effect on the cell viability, indicating that tectorigenin and irigenin were not cytotoxic to the murine macrophages. Conclusion: Our data suggest that tectorigenin and irigenin possess anti-inflammatory functions, and may provide an alternative strategy for reducing inflammation.