Involvement of cytokines in the hepatic expression of metallothionein by ursolic acid

Ursolic acid (UA), a pentacyclic triterpene acid, is reported to have inducing activity of hepatic metallothionein (MT) which responsible for the detoxification of heavy metals; however, the mechanism underlying its effects is poorly understood. To further determine the underlying mechanism of UA, this study investigated the effects of UA on the induction of hepatic MT expression in an in vitro model, using murine hepatoma cell line Hepa-1c1c7 and murine macrophage cell line RAW 264.7 cell cultures. The UA added directly to Hepa-1c1c7 cells had no effect on MT induction. However, MT and its mRNA levels were markedly increased when Hepa-1c1c7 cells were cultured with UA-treated conditioned media from RAW 264.7. Concomitant treatment with UA and pentoxifylline, a TNF-α synthesis inhibitor, to RAW 264.7 cells decreased the effects of UA on the MT induction. In UA-exposed RAW 264.7 cell cultures, TNF-α and IL-6 production and TNF-α and IL-6 mRNA levels increased. When antibodies to TNF-α or/and IL-6 were added to UA-treated conditioned media from RAW 264.7, the MT induction activity was inhibited. These results demonstrate that UA induces hepatic MT expression through TNF-α and IL-6 released from UA-activated macrophages, which may be the mechanism, whereby UA elicits its biological effects.