Silymarin Protects Pancreatic beta-Cells against Cytokine-Mediated Toxicity: Implication of c-Jun NH sub(2)-Terminal Kinase and Janus Kinase/Signal Transducer and Activator of Transcription Pathways

Silymarin is a polyphenolic flavonoid that has a strong antioxidant activity and exhibits anticarcinogenic, antiinflammatory, and cytoprotective effects. Although its hepatoprotective effect has been well documented, the effect of silymarin on pancreatic beta-cells is largely unknown. In this study, the effect of silymarin on IL-1beta and/or interferon (IFN)-g-induced beta-cell damage was investigated using RINm5F cells and human islets. IL-1beta and/or IFN-g induced cell death in a time-dependent manner in RINm5F cells. The time-dependent increase in cytokine-induced cell death appeared to correlate with the time- dependent nitric oxide (NO) production. Silymarin dose-dependently inhibited both cytokine-induced NO production and cell death in RINm5F cells. Treatment of human islets with a combination of IL-1beta and IFN-g (IL-1beta+IFN-g), for 48 h and 5 d, resulted in an increase of NO production and the impairment of glucose-stimulated insulin secretion, respectively. Silymarin prevented IL- 1beta+IFN-g-induced NO production and beta-cell dysfunction in human islets. These cytoprotective effects of silymarin appeared to be mediated through the suppression of c-Jun NH sub(2)-terminal kinase and Janus kinase/signal transducer and activator of transcription pathways. Our data show a direct cytoprotective effect of silymarin in pancreatic beta-cells and suggest that silymarin may be therapeutically beneficial for type 1 diabetes.