Silymarin, a polyphenolic flavonoid antioxidant, is known to have anti-inflammatory, hepatoprotective, and anticarcinogenic effects. In the present study, we report anti-septic and anti-atherogenic activity of silymarin. This study showed that silymarin protected mice against LPS-induced sepsis. In this model of sepsis, silymarin improved the rate of survival of LPS-treated mice from 6% to 38%. To investigate the mechanism responsible for anti-septic effect of silymarin, we examined the effect of silymarin on the production of inflammatory mediators, including nitric oxide (NO), Interleukin-1β(IL-1β), prostaglandin $E_2 (PGE_2)$, and tumor necrosis factor-α(TNF-α). Silymarin dose dependently suppressed the LPS-induced production of NO in isolated peritoneal macrophages and RAW 264.7 cells, a murine macrophage-like cell line. Also, LPS-induced production of IL-1β and $PGE_2$ in isolated mouse peritoneal macrophages and RAW 264.7 cells. However, TNF-α production was not affected in LPS-stimulated macrophages. Consistent with these results, mRNA expression of iNOS, IL-1β, and COX-2 was significantly abrogated by silymarin in LPS-stimulated RAW 264.7 cells and TNF-α mRNA level was not affected by silymarin treatment. To further investigate the mechanism responsible for the inhibition of gene expression of inflammatory mediators by silymarin, we examined the effect of silymarin on LPS-induced nuclear factor-κB (NF-κB)/Rel$ activation, which regulates various genes involved in immune and inflammatory response. In RAW 264.7 cells, the LPS-induced DNA binding activity of NF-κB/Rel was significantly inhibited by silymarin, and this effect was mediated through the inhibition of the degradation of inhibitory factor-κB-α (IκB-α)$. NF-κB/Rel -dependent reporter gene expression was also suppressed by silymarin in LPS-stimulated RAW 264.7 cells. Further study showed that silymarin suppressed the production of reactive oxygen species generated by $H_2O_2$ in RAW 264.7 cells. Collectively, these results suggest that silymarin inhibits NO, IL-1β, and PGE2 production and their mRNA expression by inhibiting NF-κB/Rel activation. Furthermore, the radical-scavenging activity of silymarin may explain its inhibitory effect on NF-κB/Rel activation.
Silymarin has been known to have anti-atherogenic activity, and it is reported that this was mediated by inhibiting cholesterol biosynthesis. However, inflammatory response is now regarded as a crucial process for the development of atherosclerosis. To investigate the mechanism responsible for the anti-atherogenic activity of silymarin, we examined the effect of silymarin on monocyte adhesion to endothelial cells and the production of proinflammatory cell adhesion molecules, such as VCAM-1, ICAM-1, and E-selectin. THP-1 cell adhesion to human umbilical vein endothelial cells (HUVECs) stimulated with TNF-α was completely blocked by silymarin. Also, TNF-α-induced production of sVCAM-1, sICAM-1, and sE-selectin was significantly suppressed by silymarin treatment in HUVECs. Moreover, silymarin inhibited the mRNA expression of VCAM-1, ICAM-1, and E-selectin in TNF-α-stimulated HUVECs. To further investigate the mechanism responsible for this effect, we examined the effect of silymarin on NF-κB/Rel DNA binding in HUVECs. Consistent with previous results, silymarin abrogated TNF-α-induced NF-κB/Rel DNA binding in HUVECs. In summary, these results suggest that anti-atherogenic activity of silymarin is mediated by the inhibition of NF-κB/Rel activation and concomitant inhibition of gene expression of cell adhesion molecules, including VCAM-1, ICAM-1, and E-selectin.