Eleutherine americana Merr. et Heyne (Iridaceae) has been used as a folk medicine for the treatment of coronary disorders and wound-healing. In our previous phytochemical study, several pyranonaphthoquinoids, including (-)-isoeleutherin, were isolated from the bulbs of E. americana. Because inhibitors of inducible nitric oxide synthase (iNOS) might be useful as anti-inflammatory agents, we investigated the potential of pyranonaphthoquinoids to inhibit iNOS activity. We found that (-)-isoeleutherin inhibits lipopolysaccharide (LPS)-stimulated induction of nitric oxide (NO) in a dose-dependent manner (IC50 = 7.4 μM). Using western blots and reverse transcription-polymerase chain reaction, we showed that (-)-isoeleutherin suppresses the expression of iNOS protein and mRNA. In addition, (-)-isoeleutherin inhibited the expression of various cytokines such as interleukin-1β and interferon-β. Activation of the transcriptional activity of NF-κB by LPS was also inhibited by treatment with (-)-isoeleutherin, suggesting that (-)-isoeleutherin-mediated suppression of iNOS expression is associated with the regulation of transcription factor NF-κB. These findings suggest that (-)-isoeleutherin might be a novel anti-inflammatory agent, and that it may work by inhibiting NFkB activation in macrophages.
Bibliographical noteFunding Information:
This work was supported by grant no. R15-2006-020 from the National Core Research Center (NCRC) program of the Ministry of Education, Science & Technology (MEST) and the Korea Science and Engineering Foundation (KOSEF) through the Center for Cell Signaling & Drug Discovery Research at Ewha Womans University.
- Eleutherine americana
- Inducible nitric oxide synthase (iNOS)
- Nitric oxide (NO)
- Nuclear factor kappa beta (NF-κB)