Mixture effects of dietary flavonoids on steroid hormone synthesis in the human adrenocortical H295R cell line

Humans are exposed to a mixture of dietary flavonoids with a variety of potential beneficial and harmful effects. Flavonoids are endocrine disruptors, acting both at receptor level and by interfering with steroid hormone synthesis. Due to a high dietary intake and the potential to cause mixture effects, assessment of combined exposure of flavonoids is required. We have studied effects on cortisol, aldosterone, testosterone and oestradiol secretion of the individual isoflavones daidzein and genistein, the flavone apigenin and the mixture of the three flavonoids in human adrenocortical H295R cells. The most vulnerable targets of the flavonoids were the secretion of cortisol and testosterone, which were inhibited by daidzein and genistein with IC50 values below 1 μM. An equimolar mixture of the flavonoids caused inhibition of cortisol, aldosterone and testosterone secretion in an additive manner. The observed mixture effect was described well by both concentration addition (CA) and independent action (IA) prediction models. Both prediction models underestimated the effect on oestradiol secretion. We conclude that the three flavonoids exhibit specific effects on steroid hormone secretion. A mixture of the flavonoids caused additive effects emphasizing the need to assess flavonoids together as a group. The prediction models are valuable tools for mixture assessment.