Suppression of inducible nitric oxide synthase expression by nyasol and broussonin A, two phenolic compounds from Anemarrhena asphodeloides, through NF-κB transcriptional regulation in vitro and in vivo

Anemarrhena asphodeloides is widely used in traditional Chinese medicine, and is known to possess antidiabetic and anti-inflammatory properties. Because inducible nitric oxide synthase (iNOS) plays an important role in inflammation, we investigated the inhibitory effects of two known phenolic compounds, nyasol (1) and broussonin A (2), from A. asphodeloides, on iNOS and its plausible mechanism of action. Compounds 1 and 2 exhibited inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells. Compounds 1 and 2 also suppressed the expressions of iNOS protein and mRNA. Moreover, compounds 1 and 2 suppressed the expression of inflammatory cytokines such as interleukin-1β (IL-1β) and interferon-β (IFN-β). They also inhibited the transcriptional activity of NF-κB and degradation of IκB-α, as well as the activation of Akt and ERK in LPS-stimulated RAW 264.7 cells. In in vivo animal model, compounds 1 and 2 significantly inhibited TPA-induced mouse ear edema. These results suggest that 1 and 2 suppress LPS-stimulated iNOS expression at the transcriptional level through modulating NF-κB and down-regulation of the Akt and ERK signaling pathways. Taken together, these findings indicate that the suppressive effects of 1 and 2 on iNOS expression might provide one possible mechanism for their anti-inflammatory activities.