The antioxidant activity of daidzein metabolites, O-desmethylangolensin and equol, in HepG2 cells

Daidzein and its glycoside form daidzin, are known to have potential health benefits and are metabolized to O-desmethylangolensin (O-DMA) and equol following consumption. In the current study, the antioxidant activity and cytotoxicity of O-DMA, equol, daidzein and daidzin was investigated and their effects on HepG2 human hepatocelluar carcinoma cells were compared. For cytotoxicity assays, lactose dehydrogenase (LDH) release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-based cell viability, cells were exposed to various concentrations of each compound (5-200 M) for 24, 48 or 72 h. O-DMA and equol did not affect LDH release, but higher concentrations (<75 M) showed inhibition of cell growth. By contrast, daidzein and daidzin (200 M) increased LDH release and cell growth. All compounds stimulated catalase and total superoxide dismutase (SOD) (CuZn- and Mn-SOD) activity, and mRNA and protein expression. This phenomenon was most pronounced for O-DMA and equol, as their effects were similar. These data suggested that O-DMA and equol possess greater antioxidant properties compared with daidzein and may, thus, be beneficial for human health.