Differential biological activity of daidzein and equol
School of Applied Science

The effects of bioavailability and metabolic transformation on the biological activities of daidzein are relatively unknown. The effects of daidzein, dihydrodaidzein and equol at physiologically relevant concentrations on the production of leukotriene B4 and F2-isoprostanes, and myeloperoxidase enzyme activity in freshly isolated human neutrophils were examined. Equol, at physiological concentrations, inhibited leukotriene B4 production (IC50 ~ 200 nmol/L) in human neutrophils significantly more than daidzein and dihydrodaidzein (IC50 values > 1,000 nmol/L). Daidzein, dihydrodaidzein and equol did not affect the enzymatic hydrolysis of leukotriene A4 to leukotriene B4, suggesting that they exerted their inhibitory effects on the 5-lipoxygenase activity. Daidzein (IC50 ≈ 600 nmol/L) protected against free-radical peroxidation of arachidonic acid significantly more than did equol and dihydrodaidzein (IC50values > 1,000 nmol/L). Equol also showed significantly greater inhibition of myeloperoxidase activity (IC50 ≈ 450 nmol/L) when compared to daidzein and dihydrodaidzein.