Cardamonin suppresses nitric oxide production via blocking the IFN-γ/STAT pathway in endotoxin-challenged peritoneal macrophages of ICR mice

Abstract

Aims: Overproduction of nitric oxide (NO) from inducible NO synthase (iNOS) plays many pivotal roles in various inflammatory diseases. In this study, we examined the effects of 6 flavonoids on lipopolysaccharide (LPS)-induced NO generation in macrophage (Mφ), and addressed molecular mechanisms of cardamonin.

Main methods: Suppressive effects on NO generation in vitro were assayed in LPS-stimulated macrophages (Mφ). In vivo anti-inflammatory activity was evaluated with LPS-challenged ICR mice. Mechanistic analyses were done by ELISA, Western blot, RT-PCR, etc.

Key findings: Cardamonin, a chalcone, exhibited pronounced suppressive activity, while pinocembrin, a counterpart flavanone, was much less active. Administration of cardamonin (0.02-2 mg/kg body weight) significantly decreased NOx concentrations in the sera from LPS-challenged ICR mice. This efficacy was superior to that of curcumin, a well-known anti-inflammatory agent present in turmeric. Cardamonin down-regulated iNOS mRNA expression and suppressed activation of STAT-1, but not nuclear factor kappaB, both of which are transcription factors for the iNOS gene in peritoneal Mφ of ICR mice. Interferon (IFN)-γ was identified as the major cytokine which mediates LPS-induced STAT-1 activation and resultant iNOS expression. Intriguingly, cardamonin suppressed the activation of not only STAT-1 but also STATs-2, 3 and 4. The involvement of the JAK/STATs pathway in NO generation was suggested because its specific inhibitor, AG490, decreased NO generation.

Significance: Cardamonin was identified to be a unique phytochemical that targets the production of IFN- and thereby suppresses the STAT pathway for mitigating inflammation.