Silibinin induces protective superoxide generation in human breast cancer MCF-7 cells

The pharmacological activity of polyphenolic silibinin from milk thistle (Silybum marianum) is primarily due to its antioxidant property. However, this study found that silibinin promoted sustained superoxide (O-2(center dot-)) production that was specifically scavenged by exogenous superoxide dismutase (SOD) in MCF-7 cells, while the activity of endogenous SOD was not changed by silibinin. Previous work proved that silibinin induced MCF-7 cell apoptosis through mitochondrial pathway and this study further proved that O-2(center dot-) generation induced by silibinin was also related to mitochondria. It was found that respiratory chain complexes I, II and III were all involved in silibinin-induced O-2(center dot-) generation. Moreover, it was found that silibinin-induced O-2(center dot-) had protective effect, as exogenous SOD markedly enhanced silibinin-induced apoptosis.