Involvement of cytokines in the hepatic metallothionein expression by alpha-hederin

Alpha-hederin, a triterpenoid saponin, has been reported to induce hepatic metallothionein (MT). However, the mechanism underlying its effects is unknown. This study investigated the effects of alpha-hederin on the regulation of MT expression in an in vitro model using the murine hepatoma cell line, Hepa-1c1c7, and the murine macrophage cell line, RAW 264.7. Alpha-hederin that was added directly to Hepa-1c1c7 cells had no effect on MT induction. However, MT and its mRNA levels increased markedly when the Hepa-1c1c7 cells were cultured with the alpha-hederin-treated, conditioned medium from the RAW 264.7 cells. Co-treating the RAW 264.7 cells with alpha-hederin and pentoxifylline, a TNF-alpha synthesis inhibitor, resulted in decreased effects of alpha-hederin on MT induction. In the alpha-hederin-exposed RAW 264.7 cell cultures, production and mRNA levels of TNF-alpha and IL-6 were increased. Accordingly, it was found that the MT induction activity was inhibited when antibodies to TNF-alpha and/or IL-6 were added to the alpha-hederin-treated, conditioned medium from the RAW 264.7 cells. These results suggest that the upregulation of MT expression by alpha-hederin is mediated by TNF-alpha and IL-6.