Effects of medicinal plant ipe on expression of inducible nitric oxide synthase in inerleukin-1β-stimulated Hepatocytes

Background : The traditional medicine ipe is thought to have various pharmacological actions including anticancer and anti-inflammatory activities. However, there is little scientific evidence to demonstrate the organ-protective effects of ipe. The prevention of nitric oxide (NO) production in inflamed livers by inducible NO synthase (iNOS) is an indicator of liver protection. We examined proinflammatory cytokine-stimulated hepatocytes as a simple “ in vitro liver injury model” to determine ipe’s liver-protective effects of ipe and clarify its mechanisms. Methods: Primary cultured hepatocytes were treated with interleukin (IL)-1β in the presence or absence of ipe. The induction of iNOS and its signal pathway were analyzed. Results: Ipe inhibited the production of NO stimulated by IL-1β and showed the greatest effect (more than 90% inhibition) at 2 mg/ml. Ipe decreased iNOS protein and mRNA expression. Ipe decreased NF-κB activation (its translocation to the nucleus and DNA binding), although there was no effect on IκBα degradation. Ipe inhibited Akt activation, followed by decreased the type I IL-1 receptor mRNA and protein levels. Transfection experiments revealed that ipe decreased both activities of iNOS promoter transactivation and mRNA stability. In support of the latter observation, ipe inhibited the expression of the antisense transcript of the iNOS gene. Conclusion: Ipe blocked IκB kinase and phosphatidylinositol 3-kinase/Akt signal pathways, which caused the reduction of iNOS mRNA synthesis and its stability. This resulted in the inhibition of iNOS induction and NO production. Ipe may have a potent beneficial effect against NO-mediated injury in organs including the liver. Key words : ipe, inducible nitric oxide synthase, liver injury, primary cultured hepatocytes, nuclear factor-κB, the type I interleukin-1 receptor, iNOS antisense transcript