Diosgenin inhibits macrophage-derived inflammatory mediators through downregulation of CK2, JNK, NF-κB and AP-1 activation

Diosgenin is a precursor of steroid hormones, which can be found in several plant species. Diosgenin has been shown to have a variety of biological activities including anti-inflammatory activity, but through a mechanism that is unclear. Especially, the effect of this agent on macrophage function has not been characterized in detail. In the present study, we examined the effects of diosgenin on the production of inflammatory mediators in lipopolysaccharide (LPS)/interferon γ (IFN-γ)-activated murine macrophage. Macrophages pre-exposed to diosgenin (0.1-10μM) were stimulated with LPS/IFN-γ. Pretreatment with diosgenin resulted in the inhibition of NO production and inducible nitric oxide synthase (iNOS) protein and mRNA expression in a concentration-dependent manner. In addition, diosgenin inhibits production of reactive oxygen species (ROS), interleukin-1 (IL-1), and IL-6, but not that of tumor necrosis factor-α (TNF-α). Inhibition of these inflammatory mediators appears to be at the transcriptional level, since diosgenin decreased LPS/IFN-γ-induced NF-κB and AP-1 activity. Diosgenin blocked CK2 activation and phosphorylation of c-Jun NH₂-terminal kinase (JNK), but not that of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1/2 (ERK 1/2). These results indicate that the inhibition of these signaling molecules expression was correlated with the reduced production of inflammatory mediators in macrophages. Taken together the present data suggest that diosgenin reduces the production of inflammatory meditators by inhibiting LPS/IFN-γ-triggered CK2, JNK, NF-κB and AP-1 activation, thereby implicating a mechanism by which diosgenin may exert its immunosuppressive effects.