Inhibition of TNF-alpha and IL-6 production by Aucubin through blockade of NF-kappaB activation RBL-2H3 mast cells.

Antigen (Ag)-stimulated mast cells induce synthesis and production of cytokines including tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 with proinflammatory and immune regulatory properties. Expression of TNF-alpha and IL-6 was regulated by a transcription factor, nuclear factor (NF)-kappaB. The iridoid glycoside, aucubin, has been found as a natural constituent of many traditional oriental medicinal plants. We studied the effect of aucubin on the TNF-alpha and IL-6 expression in Ag-stimulated rat basophilic leukemia (RBL)-2H3 mast cells. We show that aucubin inhibited Ag-induced TNF-alpha and IL-6 production and expression in a dose-dependent manner with IC(50) of 0.101 and 0.19 microg/ml, respectively. Maximal inhibition of TNF-alpha and IL-6 production was 73 +/- 4.3% and 88.8 +/- 5%, respectively. Aucubin also inhibited Ag-induced nuclear translocation of p65 subunit of NF-kappaB and degradation of IkappaBalpha. Inhibition of NF-kappaB activation by aucubin might be specific since activator protein-1 binding activity was not affected. In conclusion, these results suggest that aucubin is a specific inhibitor of NF-kappaB activation in mast cells, which might explain its beneficial effect in the treatment of chronic allergic inflammatory diseases.