Involvement of heme oxygenase‐1 in the anti‐inflammatory activity of Erigeron annuus L. extracts on the expression of inducible nitric oxide synthase in RAW264.7 macrophages

Abstract

The genus Erigeron is a member of the Compositae (Asteraceae) family and contains more than 400 species. Erigeron annuus L. is an indigenous weed from eastern North America widely found in early‐successional communities in fields. This species is also commonly found all over Korea. Erigeron annuus L. has been used in traditional herbal medicine for the treatment of indigestion, enteritis, epidemic hepatitis and hemauria. This study is to elucidate the involvement of anti‐inflammatory heme oxygenase‐1 (HO‐1) in the inhibitory activity of a Erigeron annuus L. flower (EAF) extract on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression in lipopolysaccharide (LPS)‐stimulated RAW264.7 macrophages. Cell viability and NO assay were performed. In addition, iNOS expression was detected by Western blotting. HO‐1 expression was also evaluated by Western blotting, and blocking HO‐1 activity on NO production was performed. The EAF extract at the highest concentration (200 μg/ml) significantly inhibited NO production by approximately 85% and suppressed iNOS protein expression by approximately 90% compared to LPS‐stimulated cells. The EAF extract induced the expression of HO‐1 in a dose‐dependent manner, and blocking HO‐1 activity abolished the inhibitory effects of the EAF extract on NO production. These results suggest that a EAF extract has potent anti‐inflammatory activity in RAW264.7 macrophages involving the induction of HO‐1.