Edaravone prevents iNOS expression by inhibiting its promoter transactivation and mRNA stability in cytokine-stimulated hepatocytes

Edaravone has an anti-inflammatory effect in experimental models of various organ injuries. We reported that edaravone reduces the induction of inducible nitric oxide synthase (iNOS) as well as pro-inflammatory cytokines in endotoxin-treated rats with partial hepatectomy, leading to the prevention of liver injury. Studies were performed to investigate the mechanisms involved in the inhibition of iNOS expression by edaravone in hepatocytes. Primary cultured rat hepatocytes were treated with interleukin (IL)-1β in the presence or absence of edaravone, and iNOS and its signal were analyzed. Edaravone decreased the expression of iNOS mRNA and its protein stimulated by IL-1β, resulting in the reduction of NO production. Edaravone inhibited the activation of transcription factor NF-κB through IκB degradation and the up-regulation of type I IL-1 receptor through PI3K/Akt activation, which are essential signals for iNOS induction. Further transfection experiments with iNOS promoter-luciferase construct having iNOS 3′-UTR revealed that edaravone decreased the stability of iNOS mRNA. In support of this observation, edaravone decreased the expression of iNOS antisense-transcript, which stabilizes iNOS mRNA by interacting with its 3′-UTR and RNA-binding protein. Edaravone may inhibit the induction of iNOS gene expression at steps of promoter transactivation and mRNA stabilization in cytokine-stimulated hepatocytes.