Silymarin inhibits cytokine-stimulated pancreatic beta cells by blocking the ERK1/2 pathway

We show that silymarin, a polyphenolic flavonoid isolated from milk thistle (Silybum marianum), inhibits cytokine mixture (CM: TNF-α, IFN-γ, and IL-1β)-induced production of nitric oxide (NO) in the pancreatic beta cell line MIN6N8a. Immunostaining and Western blot analysis showed that silymarin inhibits iNOS gene expression. RT-PCR showed that silymarin inhibits iNOS gene expression in a dose-dependent manner. We also showed that silymarin inhibits extracellular signal-regulated protein kinase-1 and 2 (ERK1/2) phosphorylation. A MEK1 inhibitor abrogated CM-induced nitrite production, similar to silymarin. Treatment of MIN6N8a cells with silymarin also inhibited CM-stimulated activation of NF-κB, which is important for iNOS transcription. Collectively, we demonstrate that silymarin inhibits NO production in pancreatic beta cells, and silymarin may represent a useful anti-diabetic agent.